There are prepaid jeeps and private jeeps at Bagdogra airport that will take you anywhere you like. As my flight was delayed, I had only an hour and a half to catch the toy train so I decided to take the whole jeep for myself. The guy offered to take me up to Kurseong for 900 rupees which is a bit much but it was in my budget. I took his jeep because he said I wouldn't have to pay a thing if we missed the train and although it usually takes around hour and a half to two hours, he said he could get me there in an hour.
To make the story short, we didn't make it but I gave him 400 rupees nonetheless. I know that the drivers usually give false promises but this one would actually make it if he hadn't have lost time at the gas station and if there hadn't have been a huge traffic jam right at the entrance to Kurseong. He used a bunch of shortcuts but unfortunately lady luck wasn't on our side.
Just for the info, one seat in a shared jeep is 90-150 rupees but you do have to wait for the jeep to get full. Also, don't pay for the gas or any expenses before you get to your destination. The price is the same if you decide to go directly to Darjeeling.