We just got back last night after flying to Disney for a week out of Plattsburgh NY on Allegiant. I'd never tried them before but when I found a price of $110 return including taxes I figured I didn't have anything to lose.
Plattsburgh airport was about a 3 hour drive from Ottawa. It's a tiny, but new facility on the outskirts of town. Parking was free(!) and it took about 20 minutes to get parked, through the terminal, check in, through security and to the gate. A very pleasant experience.
The flight was nothing special but it wasn't bad either. An older MD80 but it was still comfortable no-frills service (seats don't even recline which is nice that the person in front of you doesn't recline, but not so nice if you want to recline).
We arrived at Sanford airport in Orlando 2:45 later. Sanford was another nice treat. 15 minutes to deplane, get luggage and get the rental car. It takes maybe 15-20 minutes longer to drive from Sanford than what it takes from MCO, but you make that time up in the time it takes to get through MCO.
All in all, I highly recommend this option and will definitely do it again.