Whats a hobby/craft that you wouldn't expect that has an incredibly high ceiling either monetarily or in sheer skill?
For example, I'm sure the average joe doesn't know just how expensive calligraphy pens can be, or how deep the rabbit hole goes on video game speedruns.
Rock climbing.
To start out you basically just need $150 worth of shoes and some $5 chalk. Trad climbing or big wall climbing can be 5 figures and a dozen years worth of experience.
And the skill ceiling is probably obvious, but it's become an Olympic sport for a reason.
I think rock climbing has a fairly interesting cost curve, you're right.
Bouldering in the gym: Membership fees, shoes, chalk bag.
Bouldering outside: Crash pad, gas to crag, shoes, chalk bag.
Sport climbing in the gym: Rope, belay device, shoes, chalk bag, membership fees.
Sport climbing at the crag: Rope, belay device, quickdraws, shoes, chalk bag, gas to crag
Trad climbing: Rope, belay device, rack, shoes, chalk bag, gas to crag
And then if you add ice climbing and mountaineering you're really screwed. Thousands of dollars in goretex, travel, supplies, rescue kits, avalanche training, etc
Mountaineering was the next level I couldn't afford to join my friends on.
This is how a friend of mine got into ice climbing. They went to work as a glacier guide and got a avalanche training for free. They work to find their ice climbing hobby.
Bouldering here in the Netherlands can start pretty easily:
€ 10-15 entry
€ 5 to rent shoes, although you can bring any clean sport shoes yourself
And that's it!
You can look into buying shoes and memberships if you're really into it, but even then € 150 for shoes and € 40-60 a month for a membership is cheaper than my idea of an expensive hobby, like Magic the Gathering or PC building and gaming.