At this point, I would be thinking 3L. You should be able to pick up a great motor for $500 to $800. If you're handy, you can save a bunch of money by doing things yourself. The 3L forum is a great source of info on swaps & what is needed.
For a nice overview check out
www.buckshotmotorsports.com 3L services & FAQ.
Wait!! There is a group buy proposed for Buckshot PREPPED 3L short blocks in the group buy forum. Check it out!
