I'm thinking at this point we have a design split. One configuration would be an aircraft like an Aeronca C-2. For this, you could get engines, props, and instruments for about $1,300 and could probably stay under $4,000. Most likely, fabric covered wings. Probably wooden structure and this would likely need some type of bracing. Single seat, twin 10.5 - 12.5 HP two stroke engines. Hand prop start, no electrical system. Cruise 70- 80 mph. This would be a cost reduced version of what Fisher makes. For something better, I'm thinking the price would have to go up to more like $6,000-6,500. For this, I think you could do aluminum structure and skin. We are looking at about the same HP with the single DLE 200 engine but it does have electric start. You would have to keep the weight down close to 600 lbs gross to have much climb rate. The engine would run about $2,200.