I wasn't sure where to post this info, or if it'll be of help to anyone at this point, but for what it's worth: I was able to book the Tudor Hotel at the UN via Priceline tonight for $145 (and might have been able to get it for less since that was my first bid) for the weekend of the Carnegie Hall concert. If you're still looking for a hotel (or a cheaper hotel), and are comfortable bidding on Priceline, it might be worth a try. It's Midtown East (in Priceline parlance) -- a bit of a hike from Carnegie, but not too bad considering.

This also means that in the next few days (once I confirm the hotel actually has my reservation), I'll be giving up 3 rooms (shared bath) at the Upper West Side/63d Street YMCA.