Pentax MZ-30 -- Need 30x or above zoom lens for my

Hi,

I have a Pentax MZ - 30 SLR camera.

I wish to mount a 30x or bigger zoom lens on it.

I would like to know---
a) What will be the approximate price for the zoom lens.
b) Can I mount only Pentax made lenses or even the ones made by Canon or Nikon.
c) What are the options in lenses I can choose from.

Though I have an SLR, consider me only a novice please... so little explaination will be needed.

thank you very much!!