I've yet to build any of my own packs that cost more than what unipros or any other online store charges (N-cell thru Sub-C); soldering/building a pack isn't all too intimidating with the right set of tools and jigs. fwiw another cheap source for loose cells:
http://www.battlepack.com/loosecells.asp
Also, if you have the bandwidth you can d/l this VERY good video guide on building a SC Stick pack for high-amp draw applications (removing wraps, using Kapton tape). 54MB flie though, but worth the time:
http://awilletts.ezonemag.com/makepack.mpg
ops, there's a low-rez version also (11MB):
http://awilletts.ezonemag.com/makepack_low.mpg