There's a Harbortown in Fort Pierce that's also very nice that I've lived at for over a year now.
Liveaboard Marinas in this area:
Harbortown Ft Pierce: 772-466-7300
Ft Pierce municipal: 772-464-1245
Cocoa Village: 321-635-8883
Melbourne: (321) 725-9054
Sunset Bay(Stuart): 772-283-9225
Titusville: The City of Titusville, Florida - Marina Homepage
Vero Beach: (772) 978-4960
Harbortown Merrit Island: 321-453-0160
There's also Halifax Harbor up in Daytona and Indiantown has cheap rates if you don't mind being a half day inland.
This is pretty much "in season" for Florida and from Stuart on down the marinas are likely all filled up with the snowbirds that bring their boats down. Harbortown Ft Pierce should have slips open and it's a pretty nice place. Very liveaboard friendly(we have monthly pot lucks), well protected and quiet. Publix, CVS and west marine are a 10 minute walk. Prices range from $10-15 a foot depending on the length of the lease and that seems to be pretty standard for this part of Florida. Liveaboard fees in areas tend to range $50-100 in addition to the per ft slip rate.
I've visited all of the above marinas in person and have their addresses. If you need any additional info just let me know.