There is a best Western near the art museum and a sheraton near the ben franklin parkway. Honestly though? $200 per room in Center City is about what it's going to cost.

We booked the Hampton Inn at 13th and Race. It's not RIGHT in the Art Museum area, but it's $129 a night plus free breakfast for all in the AM....Not sure if when makes a difference, but we're the weekend after Memorial Day. I just did hotels.com and Windsor Suites (think it used to be The Wyndham) was $159 for a block of 8 on 31 May. Go ahead and tell the group sales folks that you got quoted $129 at Hampton for 20 rooms. Can't hurt to mention the competition. Good luck!