I can offer some advice here. There are some drawback with cheapo air mattres. First is the 4 sides tend to prop up more and this creates at least for me some very uncomfortable tension. Companies like to advertise those spots as air pillows for you head, but trust me it ain't too comfortable because they push back against ur head too hard. The center of the air mattress can also sink down more so that can create some discomfort. Those so can air springs they like to advertise on the box(that are suppose to better contour to your body) are really there to help support the structure, but the unfortunate side effect is that areas between them are more puffed up and it creates uncomfortable bumps.
Try to pick one out with the flattest looking top surface as possible and get a nice thick mattres pad. I was using a Kmart air mattress by coleman from kmart. Even though from the pictures the sides puffed up the least, it was still rather uncomfortalbe. I stuff 3 blankets, a thin foam, a very thick mattres pad, and a feather bed on it before it felt comfortable enough to sleep on...but thats just me.