Well Chapelle's Show Season 1 is averaging about 19.99 right now and is uncensored. I think it's worth the cost. South Park never seems to drop below 34.99 a season - kinda frustrating.
Insomniac releases right now are "Best of" discs. Would be much better as a season set, so I'm waiting on that one.
Those ST sets are expensive and they haven't really dropped in price.
It's a tough game to play with DVD prices. You usually need to find the right price during the week it's released while on sale, or otherwise it can be a while before a price drop. Once and a while weird good deals pop up online like the Joe set mentioned above. You're much better off starting a collection now though - a lot of catalog titles used to average 20 bucks and up a few years ago, but those same titles are usually in the 9.99 range now. And I wouldn't be concerned about availability. Barring unique circumstances, titles don't go out of print without fair warning, and even then its quite rare. Criterion Collection and some Anchor Bay discs tend to be the only real short-run discs since they license their films from studios, and rights tend to expire. Not that that's even a concern these days, since if there's any sort of demand, whoever owns the rights to a movie will slam that thing back out on disc.
Welcome to the DVD fray though Jesse, you'll soon be addicted too.
Geez, sorry, that got a little long winded.