The post o-rings (2 each post, one outside and one inside) are cheap and easy. The big o-ring around the opening is a few bucks, and often won't seal without some keg lube (but this is generally readily apparent and easily rectified). The poppets are a pain. There's probably half a dozen varieties, depending on exactly the mfg/model of your keg, and it can be hard to figure out the right one (and if the keg's been around the block a few times, there's decent chance that what's in there is wrong). And depending on the style, I've seen some LHBS's wanting up to $10 a piece (at 2 per keg). But I've had pretty good luck with the "universal" poppets you can find for $3 or so on ebay.
So for less than $15 and 15 minutes per keg, you should be set. Go for it. You certainly won't miss bottling!