"Not in supply" cards are supposed to cost $0*, as an indication that you can't buy them.
When activated, it's still worse than Fishing Village, which is $3. How about "You may reveal any number of Thingamajigs from your hand; if you do, play them"? That just gives you more actions, no extra cards. In fact you could have it so that you can play Thingamajigs that you draw with other Thingamajigs, and it would still only be extra actions.