your going to have to commit a bit more money than that to this project
a 1JZGTE is prob your best bang for buck engine and that will cost you $3000 for a front cut (giving you engine,gearbox and most things needed for conversion) then add labour
a 2JZGTTE will cost more like $4500 for a front cut plus labour to install
a SR20DET will cost not quite $3500 for front cut
a VH45 (nissan V8) approx $2800, a 1UZFE (Toyota V8) around $2000
in fact you wont find a decent motor (front cut) for under $2000 then you gotta add the costs of puting it into you BMW
so like i said your gonna have to be prepared to spend a little more than 1000 bucks, actually most of your budget will be taken up by the engine conversion
sorry to be the messenger of bad news
RellikZephyr