Avista:
I'm pretty sure that Enterprise would be the ones to talk to, as they seem to always offer good one-way one-day rentals. I don't think they have a location specifically at the Tampa cruise terminal, but I'll bet there is a location closer than the airport.
And remember "they'll pick you up" should also apply to dropping you off.
Why not stop by their office on Lake Sumter Landing and talk to them?
14 days at $14 is $196. Surely two one-day rentals would be less. Sounds like a fun cruise. I sailed the
Ryndam out of San Diego in November 2003. I think she's been refurbished since.
SWR