I know for a fact that an S15 engine and transmission is around 4k alone (not even considering a front clip!) You also NEED an S15's LSD b/c of the speed sensor being there. And buying a front clop DOES NOT mean that you get the exterior stuff (headlights, fenders, hood, bumper, etc...) Sure, you migh get some of those (who knows what condition they are in though) but I wouldn't bet on it. And lastly, even with a 'complete' S15 clip (all body parts included) I believe that it still won't 'bolt up' to the 240's frame... Which means more fabrication!
So, if you really want that set up find an S15 engine & transmission ($4k), Look long and hard for an S15 LSD(who knows how much $, and buy an S15 front conversion kit ($3k)
So there you are looking at about $8k - $9k.. Just in parts! So inless you plan on doing the installing and tuning yourself add a VERY HIGH installation price to that, say another $5k - $10k (most shops charge more for installation than the parts cost, don't know why just my experience...)
P.S.
http://www.heavythrottle.com has S15 engines and trannys most of the time that I go to their site.... Don't know about the clips though.