Vendor maps.

SSF

Once you've cleared a map level. They should be unlimited from Dori.

Its incredibly stupid to run players out of maps, and then force them to farm them back up to get to where they were.

Players will just stop playing, don't be stupid.

Gold cost is fine, they shouldn't be free; but you should never have to fight your way back to a map level.

If you're worried about glass cannon success- well thats a balance issue, not a map issue.