there's not really a "kit" (although some crappy compaines do sell them that way), but you have to piece together the JDM S15 headlights, 13 to 15 conversion fenders, a S15 bumper, and a S15 hood.
if you take the cheap way out (buying fenders and bumpers from brands like vis, raceonusa, etc), you can get all the parts for around $2k but then you'll end up having to pay quite a few hundred dollars to make the fenders fit correctly. if you take the pricey road (getting stuff from masa, gp sports, OEM nissan japan, etc) you can easily pay over $3k but you'll probably end up with a much cleaner conversion and better made parts that fit easier.
also, you'll have to pay for paint/body work which can be a lot (i'd guess $500-$800), so in the end this can be a pricey little venture (unless you lived in japan - damn you ian!!!

). i wanted to do it on my car but i figure $5k can be spent better on other things right now.