A one-way rental from TPA to an onsite drop-off in the WDW area will typically be more expensive than a round trip rental (back to TPA).
Some companies have what seems like a good rate until you realize that they are adding a one-way surcharge so you will want to compare the "bottom line" pricing.
There are a few companies in the area around Disney Springs (Hertz,
Avis,
Budget, Dollar and Alamo to name a few)
I would check the rental price for each to get an idea of best price/location for your needs.
FYI: Sometimes a one-way rental can cost more than several days or even a weekly rental round trip rental (from the airport).
I would try pricing it out both ways.