Many of the violin makers only sell their instruments directly to clients, without any shops in between. You should be able to find most of them in the instruments section.

What do you consider "affordable"? You may find electric violins for just a few hundred euros/dollars, but then you get what you pay for. You could have a look at the Fender or Yamaha instruments, they are somewhere in between and widely available. Most custom / handmade instruments go well above 1000 dollars.

You could also have a look on Ebay, there are sometimes great deals.

You can also find some electric violin shops through Google. I don't have experience with any of these.

Up to 2000 seems affordable for me.

Before buying any ebay- stuff please check the following items:

Shape:
- choose between various solidbody and skeletal instruments – but - "achtung, baby":
- certain instrument shapes are instable, tend to bend, won’t stay in tune (the treble clef shaped “things”) or were reported to break (the big S shaped products).
- If your favourite instrument has an uncommon shape – is a special shoulderrest provided? How does it fit and feel?

Wood materials and manufacture:
- neck: polished?, laquered? – how does it feel?
- fingerboard: ebony? hardwood or softwood painted black? plastic? - corrugated or even?: look along it against light

- pegs: ebony? hardwood painted black? plastic? - do they fit properly / stay in tune? – if possible test with peg compound: where it sticks to the peg after turning it several times, there is no contact to the peghole.

- Body: weight? Top-heavy? Does your favourite shoulderrest fit / does the instrument’s (rudimentary) ribs have a rim?
- the bridge is often roughly cut (esp. the feet) and a bit too high – this is fine: your luthier can adapt it to your needs (see below!).

Projection:
- is the angle neck to body OK? – measure from mid-upper-edge end of fingerboard down to the body: flat-top solidbodies or skeletals: approx. 26 mm, semiacoustics: approx. 20 mm.
- too flat projection may cause instability.
- the bridge / the strings-to fingerboard distances may be too high – in some cases a luthier cannot cut down the bridge enough (not enough wood above the heart) to make playing comfortable for you: the instrument will need a new bridge.

Pickup (transducer) / electronics:
- test your future new instrument thoroughly. It should sound fine with a STANDARD guitar amp, (Fender tube amp) when you cut the treble control frequencies on the amp a bit (because of “the screachies”: frequent piezo disease).
- most cheap up to mid-price e-violins are equipped with a cheap piezo transducer under the bridge (popular: Artec 8888). Some producers even replaced it with an even worse device.
- the Artec doesn’t sound THAT bad purely – but many producers have added active electronics to eliminate the well-known screechy character of many of the piezo transducer family products, improving the Artec sound to the worse (muffled and flat – no clearness / brilliance, no “ground”).
- also test the often provided onboard headphones amp – many make a lot of noise or are even distorting.
- Some instruments have a plastic electronics unit pinned to the bottom including potentiometers, jacks and a battery compartment. Mostly the components are very cheap, are not replaceable and tend to make nasty noise soon. Not reliable.
- Some semiacoustics have slider units (see above) or battery compartments “nailed” to the ribs or elsewhere without adapting them properly to the curvatures of the corresponding body parts.
- I have even seen semiacoustics with a Barcus-Berry piezo bridge installed the wrong way round (piezo element under the e-string).

Connections:
- have a look at the output jack(s): mini jack or 1/4 inch standard (guitar) phone jack? Headphones jack may be mini (mono signal to stereo) jack, output should be 1/4’’ jack.
- Where is the output jack placed? – On the right (bow arm) side the cable may tear down the instrument (weight on the wrong side) and interfere with the bow arm.

Forget the bow delivered with cheap e-violins: light the open fire with it or break it on purpose in a show – it’s too soft, often twisted, tending to bend to the wrong side etc….
Use your own fine bow (I believe you started with and are still playing a tradional acoustic violin).
Forget the cables supplied with cheap stuff: limited frequency range, bad shielding, bad plugs…
Forget the rosin – buy something serious for few money at your luthiers’.
The cases are cheap foam but do their job – as long as you don’t let it fall down with your instrument inside. Temperature isolation sometimes is better than with expensive cases.

If you have satisfactorily checked all these items, you’ll probably opt for an instrument more than USD 1000 worth: congratulations – you will surely have a lot of fun with your professional instrument.

Once again “achtung”: Big recommended music industry names don’t mean EVERYBODY is satisfied – many musicians spend a lot of money and only believe that THIS HAS TO BE IT – because of the price / the pain having spent much money. If you want to buy an instrument above USD 1000 make sure the company has an adequate return policy. You’ll probably need it, because very few serviceable instruments or almost none can be tested even in bigger music shops – only the big Y and F (last of low-mid price range) are represented here and there. See above.

If you opt for a semiacoustic instrument - go to your luthier and buy a manufactured instrument for a moderate price (USD 300 or 400). Then you'll have a fine basic material which FEELS GOOD and which you can electrify with a piezo bridge of your choice
http://www.barberatransducers.com/
http://www.headwayelectronics.com/
http://www.ashworthelectronics.co.uk/
http://www.barcusberry.com/
or with a magnetic humbucker
http://members.aol.com/bowtronics/
http://www.uli-boesking.de/rebo/
The magnetic PUs won't mute the acoustic sound of your instrument as the piezo bridges do.
Then think about building in the jack into the ribs of the violin
http://www.uli-boesking.de/rebo/inst_gal/Seiten/12moe_gr.htm
or using a Carpenter style jack.
http://www.uli-boesking.de/rebo/inst_gal/Seiten/03cze_gr.htm
Some systems need a preamp: you can buy an external one or go to a GOOD guitar repair shop and let them build the preamp in. I did it this way on one of my violins - the preamp is a custom design - not bigger as a thumbnail - fixed in the inside on the output jack. The battery compartment is adapted to the curvature and inserted into the ribs
http://www.uli-boesking.de/rebo/inst_gal/Seiten/14blu_gr.htm
http://www.uli-boesking.de/rebo/inst_gal/Seiten/13moe_gr.htm