How to make refracter telescopes ??How much the lenses must cost ?

Answer 1

That depends on how big and what quality. You can get small (~60mm) achromats or copier lenses for $20 or so, or even scrounge something for free. Or you can spend thousands on a large apochromat.

Answer 2

You can buy a kit for $9 to make a simple refractor. It will magnify 16 times and not be corrected for color error and other optical defects, but it will demonstrate how the telescope works.