That's a really broad question, and the search box is really good for answering such questions.

For 2-3 grand there aren't many Honda engines you aren't going to be able to get, except for K series or H series. Anything B series, you should be able to get an engine, tranny, ecu, and wiring harness for 1500-2500. D series or J series, same deal, but cheaper. Look around Craigslist, and go to some junkyards.