You can find corns for pretty darn cheap, plenty of pretty morphs have been bred by the dozens for years and years now, so you can find a fairly "non-wild" (pink and orange for example) for $30 at a show probably, a bit more at a pet store or from an online/local breeder. There are more expensive morphs and less expensive morphs.

As far as size goes for corns, here's a rat snake I found using google, pretty comprable to what you're looking at for a 7-8 year old corn snake that stays healthy for its whole life:
http://i213.photobucket.com/albums/c...ewithsnake.jpg

I couldn't find a good pic of a large adult corn, so that will have to do just to give you an idea. You can see, the snake is pretty darn skinny for its length, probably only weighs a couple of pounds, the guy barely looks like he has to do any lifting work to hold the snake up.

Also it will take many years for a corn to get to full grown, so you have plenty of time to get used to it growing bigger than a pencil(hatchlings are TINY!).

I highly recommend corns(or any of the other snakes mentioned here, but a corn was MY first) for a starter snake.