Like the title says, what is the least expensive audio system that you could live with and see yourself enjoying? Not just speakers, but the whole system cost (perhaps excluding cables and source player).
Here is something I think I could make do with:
Pyle PTA2 Mini 2x40 amp (assuming it works as advertised)
Monoprice MP-65RT or Dayton MK402 speakers (although I would prefer the MK442 to either, but we are talking minimal, and I could deal with the MP-65RT or MK402, especially considering there is a tone control on that amp).
Monoprice 12" sub or Dayton
SUB1200 or
SUB1000- With those speakers, I am going to need a sub. I love my bass too much to go without, and similarly priced full range speakers I do not think would have equal bass quality. I would really want to have some experience with these subs to know for sure which would be adequate though but I suspect they would be enough to do the trick. I think the 8" versions would be too badly hobbled for my tastes.
Sure, it doesn't add up to the best system in the world, but I think that could end up being a pretty listenable system in the end, with some care put into setup. The end cost would be under $300. After closely experiencing a bunch of really cheap speakers, I was surprised at how listenable they turned out to be. They were all flawed in one way or another, of course, but that didn't prevent me from enjoying music or movies when I got them going. Needless to say, I would prefer higher-end systems, but if I was on a deserted island (with a power source, likely solar panel based),I could listen to a system like this without being constantly reminded of some shortcoming that might plague an even more compromised system.