I stand by my estimate of 42. It wasn't just a stupid hitchhikers joke, it was serious.
Black Market needs to be banned, because you can just put baker in the BM deck or something. Also Haggler, as Adam brought up. Open haggler/lighthouse, hit $7 on turn 4. My current list, using the posts in this thread:
Vault, Death Cart, Chancellor, Scavenger, Baron, Develop, Poor House, Masterpiece, Baker, Secret Chamber, Storeroom, Farmland, Horse Traders, Stonemason, Cellar, Crossroads, Warehouse, Courtyard, Harvest, Mandarin, Fool's Gold, Black Market, Doctor, Menagerie, Nomad Camp, Inn, Forge, Expand, Watchtower, Salvager, Tunnel, Remodel, Remake, Upgrade, Graverobber, Procession, Butcher, Loan, Haggler, Sage.
We are already at 40, and I'm sure there are more. AdamH's 55 may be good.