Whoever said the .com was $3000 a year was scamming you. Typical registration costs for .com are maybe $10/year.
Here is who I use to buy my names:
godaddy
If it's a commercial site, it probably should be a .com. If someone already owns the name you want, just pick a variation of it. Don't pay an outrageous fee to a cybersquatter.
.org names are more appropriate if it's for a nonprofit, club, civic organization, or other not for profit type thing.
If your site is good with good content & publicity, it shouldn't matter if your domain name is catpoop.biz .... people will still find it.
To help you pick available names, sometimes nameboy has some good suggestions. Just think up some words that describe your site and plug them in:
Nameboy Ultimate Domain Name Generator, search, creation, domain name lookup and domain registration