I think it's around 100 miles. A towncar from Sanford to WDW is aound $160 return trip, so I would imagine a towncar transfer from Tampa would be a LOT more!
There's a section on the Tampa airport site that lists some limo companies that would handle the transfer. I can't find a published rate, but they all have email addresses that you could use to contact them. Click on the 'Orlando / Walt Disney World' heading on the page below:
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