What version of ArcPad do you have? ArcPad 8 and 10 both come with ArcStudio, so you are able to utilize it at no additional cost. If using ArcPad 7, then it was a separate purchase at the time. If you are using ArcPad 7, I would recommend an upgrade to ArcPad 10, which is $250 I believe and then would give you access to ArcStudio.