We have flown Allegient many years ago but not from Columbus and also not to Sanford so not sure how much this will help.
When we flew it would either be myself or SO by ourselves to Clearwater and who ever was not flying would drive up from our condo on AMI and pickup the other.
We didn't need any luggage or extras so it didn't matter and just flew them for a cheap price.
1. Allegiant charges for everything at least when we flew them (Bags, Carry-on, Seat Assignments, Early Boarding, Can of Coke)
2. Schedules matter!! Allegiant is not very flexible and will usually only offer 1-2 flights to Sanford but then they are necessarily daily flights either.
3. Are you renting a car? If so MCO will have much more selection of cars and rental car companies to shop price.
4. Are you doing private transfer or Uber/Lyft? If so Sanford will be much more expensive.
It might just be worth it for SouthWest or other airline when you factor in the above.
Other Nickel and Dime Airlines like frontier and spirit maybe cheaper and I believe they do fly to MCO.