Have you tried hotels that are downtown, but not part of the hotel block?
The Courtyard Baltimore Downtown is 1 mile away (not American, not too sure of how far that is, but should be walkable), and you get the number through the Marriott website (i think it's a comglomerate of sorts...
As usual, it's rather pricey, $250 Thurs night, and $230 for Fri and Sat
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