I think the kickstarter/indiegogo idea might work. With the tier system you could easily go with: for X amount the materials will be x, if we reach Y it will be thè more costly y... The interest might turn out to be higher than expected if properly advertised on tjc (and twitter etc) and if it's not at least it will be clear at that point how much interest there is allowing you to get better estimates how much can be spent on tooling