How much do Apple II's go for these days?
Depends on where you look. On ePay you'll find them for the $20-$120 range depending on model and options. A stock ROM 01 IIgs with no drives or anything is probably one of the cheapest options for entry level.
Ultimately though, if you're in the market for a II, you should be checking forums and Craigslist for the deals. Like the Vintage Computer Forums. Here is my rough estimate of pricing/usefulness for the Apple II line.
Apple II: ($100+, not very useful)
Apple II+ ($100+, slightly more useful, limited RAM)
Apple IIe ($20+, pretty decent for 8 bit software)
Apple IIc ($30+, portable, but not expandable)
Apple IIgs ($10+, price varies wildly based on upgrades, most powerful)
Apple III ($???, really rare, not really suited for music)