Despite the claim, there are certainly times when travel in Florida is quite affordable. For example, I just booked a midsize one-way rent from FLL to Orlando for $10.07 plus taxes/fees. That was the basic rate on Alamo...no special codes required.
That said, Orlando Vic is the bearer of bad news. Due to the huge number of folks that want to come enjoy our state in late December, the likelihood of finding a deal is low.
Be sure to look for rental car locations away from MCO. I rent a lot of one-way car rentals between Fort Lauderdale and Orlando. In Orlando, there are many rental car offices in the Disney and Universal attractions area. If your plan is to spend all of your Orlando time at theme parks, it might make sense to do a one-day rental between MIA and a local rental office. Then, take a towncar/shared-van ride to MCO on your departure date.