TBH thats a hard question to answer. How much you spend will depend on which tools you have already and what work you want to do yourself (will you outsource the heat treating or grinding or anything else?).

It'll also depend on the materials you want to use.

I'd start by reading the stickys in the Workshop forum and finding out as much as you can there. Search out threads on razor making and you could also maybe try PMing one of the razor makers with any specific questions you have.