Funding your hobby...

[AGuinness]

I've primarily funded things the same way, year-end bonuses, gifts, etc.
After I got back into the hobby, one thing that appealed to me was buying some of the important cards that were big when I was growing up but could never afford. Part of my idea was that I could potentially hold them for a while, sell at a profit and put the money back into other cards. And at times, it worked nicely - other times, not so much.
One of the cards I got early on was a T206 Speaker (Sweet Cap back), which opened the door to learning a whole lot more about T206s and pre-war stuff. That made me rethink things and started me on my T206 journey I'm still on now. I sold that first Speaker to help with my T206 project (not done yet!), and now I find it challenging to put the money I get from selling stuff into other cards I plan on selling because my PC has so much stuff I want to fill in.
A couple quick thoughts:
COMC is a great place to flip and learn lessons about flipping. I've tried various strategies (modern rookies, autos, slabs, buying wax, etc.) and figured out a few things that I prefer. While I've made plenty of dumb mistakes, I've also learned a lot and been able to cycle through funds there, reinvesting some and using some for purchases. I haven't put in any money in years, but have bought plenty of cards that now reside in my PC.
One of the biggest/best pieces of advice I took to was to buy things that you'll appreciate or like even if they lose value. In other words, if it's something you end up not being able to sell for bupkis, but you still can enjoy, that's going to be a good buy no matter what.
I do think that selling things helps with buying things, as the process helps build appreciation for what attributes matter most, certain downsides to specific cards (such as common print defects that might not be calculated into a grade) and in knowing the cost and work going into a sale.