Goofy's apprentice said:
You pass through customs while driving. Makes everything move much quicker when you land.
I couldn't agree more. The rates are substantially lower for all domestic air travel and when you leave out of BUF, that's exacty what you're doing...taking a domestic BUF to MCO flight.
Here's a perfect example. In November, our travel party was 4 adults and 1 infant (free). Our destination was Vancouver for a family gathering. The cheapest I could find in Canada was $1875 CAD return trip with Harmony Air and believe me, I checked all the options (ie. Hamilton - Abbotsford/Vancouver, London - Abbotsford/Van, Tor - Abbotsford/Van...etc).
Then I thought...

...how about BUF to Seattle and a rental car for the week to drive into Vancouver for our trip. BUF - SEA return trip with Southwest would have cost me only $850 USD and the rental for a week was booked at $200 USD (Mini-van) which is roughly the same deal we were getting in Vancouver, so the rental is a wash.

However, Canadian law prohibits Canadians from driving American-plated vehicles into our own country. Our friends to the south don't have a silly law like this and allow their tax-paying citizens to drive Canadian plated vehicles into the US. So, essentially, this law cost me about $850 CAD after the exchange is factored in.
Sorry to go off-topic there. The point is...fly out of BUF for any US trips. I got a pretty good deal flying Fri to Fri ($700 for 4 adult fares/ non-stop)