How have I curbed expensive hobbies....
Car stuff - Buying new parts and getting big brown boxes in the mail is fun but expensive. I've toned down my purchasing and spend much more time cleaning / repairing / painting parts by hand instead of buying new. I will tend to modify what I have instead of buying new. I realized I can get 95% of the result and 100% of the enjoyment out of 50% (or less) of the cost. New rims for one of my cars (Cragar S/S's) have skyrocketed in price, they are $250-300 each (used to be $150-$175). I have a set already so instead I polish out the rust pits by hand, etc. Sure they are not new but saving $800 for a little work and not 100% perfect parts is good with me. As far as painting goes, I've had extremely good luck with a good rattle can primer and "oily" rattle can top coats in satin finishes. Almost as good as powdercoat as far as durability. I pick up used parts when deals arise too. Swapped a spare bumper for my IH truck for a plow for one of my really old Cub Cadets so no money out of pocket. Guy I know needed cash fast so I got a front mount intercooler kit that normally goes for $500+ shipping for $100 (and it was still brand new). Etc.
Airplane stuff - Don't want to spend the money for flight training or building my own airplane right now so I'm building balsa models. OK this isn't even close to the same thing but as I build larger and ever more complex models a lot of it will transition to building a kit airplane (if I go wood). It's probably a poor substitute and I'll never be geeked out with RC models and such but as a temporary fix it works for me.
Equipment stuff - I NEED NEED NEED (in my mind) a Kubota BX25D (sub-compact backhoe loader). At $18k, it's not really in the cards right now. So I'm playing with a Cub Cadet 782 which is a large garden tractor. I am thinking about building a front end loader and backhoe for it (there are plans but no real kits). Total cost, $5k? For now instead of playing with something new, maximizing what I have. New tires, 3 point hitch and attachments so I can play in the yard / garden. Had a blast the other day snow plowing the driveway after I picked up an original plow for it for $125. Total cost in it, $600? Even if I spend a couple grand on attachments and upgrades, and a repaint, still about 20% of a new tractor (though I'll freely admit.... it won't have the capability of the new one!).