"if each coin is worth 1/10th its cost, nobody will mint them" No. What will happen is as the miners with the highest mining costs drop out of the network, the

"if each coin is worth 1/10th its cost, nobody will mint them" No. What will happen is as the miners with the highest mining costs drop out of the network, the difficulty target will decrease and decrease... until people stop dropping out of the network. "people make their own and the price collapses" No, again the difficulty target would adjust to regulate the rate of coin rewards. See https://en.bitcoin.it/wiki/Difficulty https://en.bitcoin.it/wiki/Difficulty