right now, each win pays out only once. It should be possible to buy the items in any order and still have enough money through wins/bounties/the final prize money (unless there's a bug preventing payout). We didn't want to make it mandatory to "grind" matches, although in hindsight maybe it would make more sense for the matches to pay the reward every time—might be something that gets patched in an update.
For now, if you somehow get soft-locked, there's the free money cheat code TRUST FUND that should make it easy to buy everything.