Did you talk to Jones, I know that he offers the daily quest Scraps for Snacks before he will offer you another quest Imprisoned Treasure. You should try that.

Side Note: I have to agree with you about the crafted schematic costing players (with OCD) 5 plat per toon if they want to complete all the quests. I know it's a marketing strat, but the mystery weap is weak when compared to the other level 50 gear out there (imo) and I hate to have to spend plat just because I'm a completionist.