I will need to get from Manhattan to JFK on a Sunday morning and was considering using a Limo service. A few of the services (Boston Coach, Gotham Limo) charge $99 for the trip; many other limo companies charge about half that--$46-$53. (Taxis seem to charge a flat rate of $35.)

So, what's to explain the disparity between the expensive limo services and the cheap ones?

Note: Price is of some consideration to me, but reliability and comfort are even more important.

[Obligatory FF data: Boston Coach, for one, does, or at least used to, offer FF miles.]