Steep?! You must be new and/or poor - 5k is less than the cost of 1 black dye, less than the cost of 1 set of good armor, etc., etc. Go on some quests/missions, pick up all the junk and gold (instead of leaving them there) & sell it to the merchant. You'll have 5k soon enough. 5k to join a real, established guild - cheap.

Scam?! A pretty slow scam. If you just want to scam people, there are better and faster ways. Even just a not-quite-scam, like buying wood and turning it into parchment, is faster than that.

P.s - and I'm not even a member of the Crusaders.