My first 200k was on a Worksman cruiser. I think Machka said she did her first few brevets on a mountain bike. I'm currently riding a Raleigh Sojourn. I just got back from a ride with one of the rando crew who rides a recumbent. We have several of our local Rando crew on Seven-brand titanium bikes (don't think they're $1,000 bikes, though). So they vary all over.
On a 600k back in the spring, I tried to take pictures of all the bike there. I missed a couple of fast guys, I think, but the rest are here:
http://s192.photobucket.com/albums/z...00kRandoBikes/
There are regional differences. Very few people around here use fenders, and the handlebar bags are not very popular, traveling light is the thing. In other parts of the country, it's just about required to have fenders and a big bag to tote your clothing.
Summary: You can ride just about anything. It would be informative to show up at a local ride and see what other people are using.
On the budgeting, you can spend $xxxx on a bike, but when you start buying good lights and cold/wet weather gear and proper bike shorts and shoes and all that stuff, you'll spend as much as you did on your bike.