Savings for me.
I got my PPL at age 17 and then plodded along gaining hours until I'd accrued enough money and hours to do a BCPL to CPL/IR Upgrade course. From BCPL to Frozen ATPL cost me about £35,000 in total in the mid-90s, that includes everything: travelling, hotels, CAA costs, etc.
No bank of Mum & Dad here, and thankfully no debts.