How much budget for bass?

I agree with what's been said here, except I think the price tag for good bass in full-range speakers starts at about $3000, closer to $5000 (new).

Again, it all depends on your budget, and if you're buying new or used. Anything under $800 used, I'd start with a good pair of two-way monitors and go from there. Add a sub later. Or later on get a pair of full-range speakers and make the monitors your surround speakers or sell them. Etc.

It depends on how your budget, your room and how good you are at shopping. The cost of good bass response is disproportionate to the amount actual bass contained in the music. That said, I sure do miss it when it's not there when it's supposed to be. If it's at all possible, it's worth trying to acquire. Is it "high end" if it's imcomplete?

You connect the subs from a 2nd pre/pro output usually.