The price depends mainly on the style of pump (external or submersible) and the quality of the brand.
For submersible, you've got your bottom end like Rio, Ocean Runner, etc, and on the top end, Danner Mag, Eheim, Quiet one, etc.
For external, there's pan world, blueline, etc on the low end, and iwaki, sequence, etc on the top end. However, quality of external pumps is usually very good regardless.
For smaller tanks, most people use submersibles. In your case I'd recommend a Mag 9.5, Eheim 1260, etc.