Having read
this thread, and looking across here, it seems the Feltham Rail-Air information is a bit out of date. The fare is probably wrong and it's also worth pointing out that if you want to go to T4 or T5 you should get the
490 bus, not the
285, which goes to T2 and T3. It may also be worth pointing out that there's a fast train from Feltham to Clapham Junction, which provides connections to loads of places south of London, as well as the Overground.