Hi deception,
The pros and cons of the different types of protectors are in post #89 here.
With a budget under $100 … I would probably suggest one of the thin membrane type of protectors such as the Protect-a-Bed (or some of the other similar brands). I would look for one where the surface fabric is either cotton or some kind of rayon fabric (to wick moisture better) and where the surface itself (not just the sides that stretches and tucks under the mattress) has a little bit of stretch as well (like a cotton jersey) so it doesn’t create a 'drum" effect on your mattress.
These are probably the most popular types of protectors and while you give up a little bit of ventilation and temperature regulation compared to the other types because they are not quite as breathable … they are thin and have little effect on the feel of the mattress and also are waterproof (vs water resistant or moisture absorbing) in normal use.
Phoenix