Bluetooth headphones should work fine. My colleague has a 1400 and is using the Bluetooth a lot these days. She has had no problems with printers, mice, and all sorts of other BT peripherals. She hasn't used a set of headphones, but I suspect they should "pair up" just fine with the Motion.
My only experience with wireless headphones was when one of the office cats chewed up the wire for my iPod earbuds, effectively making them "wireless." Funny, but they didn't work after that...
If you want to save money, perhaps you should think about NOT going wireless. If you will be viewing movies, the tablet isnt that big, so the two of you will have to be right next to each other, and close to the tablet, anyway. A cheap headphone splitter might be the solution. And can you opt for a good set of speakers for playing MP3's?
Depends on your usage, of course.