I'm a gambler, so I might buy the cheap econ fare and hope for an upgrade.

The one-way TPA-MIA-LAX fares total $1,111, but the nonstop MIA-LAX fare is $1,774, so relative bargain. It appears that the multi-city forced MIA connection isn't pricing as two separate fares, as the nonstop fare MIA-LAX is substantially more money.

The TPA-LAX nonstop is ~ $740, so not a huge premium for a much nicer seat.

First may be sold out already, as there are only 8 F seats.