Have you searched the forum, this question comes up fairly regularly. Being realistic, you will struggle to get 5 speed kit for an MTB, as everything has been at least 7 speed for the last 20 years, unless real low end, like a BSO.

For costs, even using Shimano Tourney, you would probably find it cheaper to get a new / 2nd hand bike with this fitted, rather than buying parts individually. For measuring, get a set of vernier caliper; and look on the Park tools website for how to guides.