I've made the bus transfer 2x in the last year. The shuttle operates about every 20 mins. It is about $7, if memory serves and makes a stop at the Jamaica LIRR station. It took about 45 mins (closer to an hour if you're going to BA at JFK).

Other time I was rebooked on a JFK flight and DL printed me a voucher for a car service. Took about the same amount of time total (had to wait a good 1/2 hour at LGA). There really is no good way that I could find to get the airline to pay for it, even on a AA/AA transfer YYZ-LGA/JFK-Sao Paulo.

JL