I haven't actually built a kit yet, but have a small stash of 40 kits and a few boxes of junkyard parts I got on Ebay. All tolled, probably $5-600 tied up so far, including tools and finishing supplies. When I do finally get back to building, I plan to do box stock builds at first and go from there.
Now, my primary hobby is another story. Being a woodworker/cabinetmaker, I have acquired quite an arsenal over the past 35 yrs. I probably have at least $10k in tools, accessories and supplies along with another $6-7K in lumber inventory. Now, mind you, if I was a pro, these figures could easily triple.
John