I keep books on all my expenses and hobbies are no exception; it's the best way for me to keep tabs on my spending and to remember what was spent on an item in the past. I budget a monthly allowance for hobbies, same as we do for food, mortgage, utilities, etc. All hobby expenses wait until funds are available in my "hobby account" and that gets divided up among all my hobbies. A big purchase for one hobby robs the others and as a result I'm sometimes squeezed for resources, but it does help cut down on frivilous expenses and encourages me to make purchases which are useful for multiple hobbies. Since the money in my hobby account is intended as disposable income, I don't need to justify expenses to anyone but myself.
Sometimes purchases of tooling comes from other accounts, such as the homestead account or automotive accounts, when the purchase of tooling allows a repair for less than it would cost when the job is contracted out. Frequently automotive tools, woodworking tools, etc fall in this category. If it's cheaper to let someone else do it, I let them, but it rarely is.
It's worked well for my household and as a bonus, I can query my accounts for data and trends going back years. I'm sure it sounds like a complex mess, but once it's an established habit, it takes litterally only minutes every month to keep the books current.
