To the north (near sebastian):
Key West Inn at Capt. Hiram's - looks a little pricey though with rates in the $80 to $100. 800-833-0555
The Davis House Inn - looks like a B&B, rates $60 to $80. 561-589-4114
If you go a little further north, you have oodles of options in Melbourne, including a Hampton Inn, Courtyard by Marriott, Hilton, Holiday Inn, Days Inn (Palm Bay)