Make sure the Jet Blue flight is non-stop. Sometimes they route you through Boston or JFK.
Yes, and in this case the direct flights are cheaper than connecting. The $84 flights are direct.
I had about the same price on Southwest for a January trip from BWI though - about 18 months ago - think it was $79 for most of the trip legs for everyone - that's each way. I'm assuming that $84 price quoted was each way, not RT.
Between DCA, Dullas, and BWI, there are plenty of flights available. I've actually found that Kayak is nice just because I can compare the pricing for all 3 airports at once by just picking Washington as my departing city. Unfortunately, most individual airline sites require picking a single airport which can be annoying when the airline flys out of several of them.
Now... In May I got a non-stop RT on Delta from DCA to MCO for $189 (including taxes).
And I just paid about a month ago about $275 for a RT in November on Southwest from BWI to MCO (nonstop).
Since my May purchase however, I know flight prices have gone up across the board for most flights.
Here's a little tip: when searching on travel sites, use airport code WAS. That will search all washington airports.
I just bought my January airfare from Dulles to MCO for $69 each way. They just recently adjusted their schedules for Jan/Feb, but the times work for me. The day I was coming home there were 2 non-stops, but now there's only one.