My biggest hobby expense is my boat. Small cabin cruiser but fairly complex to maintain (engine, generator, A/C, water system & water heater, flush toilet and shower, stove, fridgeetc. etc.)
I kept accurate records last year of all costs: slip rental, maintenance, fuel, taxes, insurance and upgrades. I divided this by the year's engine hours to come up with an accurate cost-per-hour of using my boat. Once I looked at the number, I deleted all the files and burned all my notes -- I never want to see THAT again.
We've had a couple of planes in the past (Cherokee, then Arrow). I still fly some, but I don't ever want another airplane. Airplanes are a good way to end up with a small fortune -- assuming you started with a large one.
When my friends ask, I tell them the best way to get your wife to agree to an expensive boat, is to buy an airplane. After a few years paying of that, she'll be thrilled to "only" pay for a cabin cruiser.
I guess our RV (Travel Trailer) is kinda costly. But it doesn't cost very much when we're not using it - just storage.