Bluetooth operates on the same set of frequencies as wifi and your sky sender, but all is not lost.
It uses a different transmission technique to wifi so the two will not interfere, so it is likely that bluetooth will not interfere with your sender.
Also, bluetooth is a short range radio technology. You can get dongles that claim to transmit for 100m, but don't forget that for it to work, both ends need a 100m range, and it is likely that the PDA doesn't.
You can have multiple devices operating through one bluetooth dongle so having the keyboard and PDA attached at the same time is possible.
If you're worried about buying a keyboard that isn't going to work in the vicinity of your sky sender, you could buy a bluetooth dongle off Ebay for around �6 and then try it out just with the PDA?