Originally Posted by platbrownguy
Cab fare would be $150 easily, maybe more.
There's a $5 shuttle from Islip to the LIRR (Long Island RR) station @ Ronkonkoma, LIRR (~$7) takes 80 minutes to NY Penn Station. Then transfer to NJ Transit to get from Penn Station to Secaucus then Hoboken (~$5?) and take the light rail from there to wherever you're going. Allow 4 hours total.
Or just fly to EWR and cab it from there.
Instead of NJ Transit, if you don't have a huge amount of luggage you'd be better off walking one block east from Penn Station to the PATH terminus at Herald Square (33rd and 6th, if memory serves). That'll take you directly to Jersey City. You may have to change trains on the PATH -- the station for the Hyatt Regency is Exchange Place, so you'll need to do a same-platform change at Pavonia/Newport.
On the other hand, remember that Southwest doesn't have change fees, and as of today, you can book tickets to EWR (if you're coming via Chicago). You'd be much better off switching your ISP ticket to an EWR one. To get from EWR to Exchange Place, take the AirTrain to the airport station, NJTransit one stop to Newark-Penn, then PATH to Exchange Place. Total cost will be about $10.