The traditional and very successful approach to getting past the brittleness of "What would you pay for this?" is to sell vaporware. It's how Micro-Soft (before

The traditional and very successful approach to getting past the brittleness of "What would you pay for this?" is to sell vaporware. It's how Micro-Soft (before the S was lowercase and the hyphen was dropped) and many others got started. You say to yourself: "I have a pretty good idea of how much work and expense it will take me to build this", then you go off and try to sell it as though it was already done or just getting polished for release. Once you have orders (or even better, cash advance!), you (privately) commit to either finish the product or cancel/refund orders if you fail^Whave a great learning experience. It's dishonest, but it works, and if you structure your offer fairly (don't induce reliance on the vaporware, only induce desire), it's not evil. Successful established authors do this before they write books. It's a standard technique in publishing. See also KickStarter.