You're leaving out the cost of the crimpers and cable ends, tester, etc, but even so, that sort cost analysis only makes sense if you're actually going to use all 500 or 1000 feet of the cable. The vast majority of people aren't, even if they wire most of their house and I seriously doubt the OP is going to need that kind of bulk supply.
If he's actually looking to re-wire his place (in-wall, etc) then learning how to make the cables makes sense. It is a useful skill. If he's just looking at replacing a few 6-20' patch cables from modem to router to PC, it only makes sense if he just wants to learn.