There are far too many variables for anyone here to tell you how much it will cost, any more than if you said "Hey, I've never built a house from scratch but I can get some cheap lumber - how much will the rest run?"

You HAVE to do a LOT of research and self-education before embarking on such a project, and it can't come just from looking at books and online resources. You have to literally get your hands dirty as well. Bikes are a mechanical device and putting one together requires at least intuitive knowledge, and in many instances specific knowledge of the mechanics, geometry and mathematics involved.

Find a cheap bike on the curb or garage sale that still works, get a book on repair/adjustment, check Park Tool, Sheldon Brown websites and numerous videos available, and THINK about what you are doing. You will never fix bikes properly if you try to learn how to do things by rote or manual alone. As I have often said - "There's no such thing as a routine repair." Just when you think something is simple is transforms into something else.

If you hit a hitch and can't figure it out post it here with full info and proper terminology and you'll get helpful responses.