Really?
The engine is, at most, 30% of the total aircraft price. If it goes up 20% on the engine cost, then that is .30/5 of the total aircraft cost, or 7.5% of the total aircraft cost. Quite honestly, if a cost increase of 7.5% is enough to close the door for you, then you didn't belong there in the first place. I'm sorry to say that, but you seriously HAVE to allow for unexpected expenses. If 7.5% tips the cart for you, then the cart was not going to survive in the first place. We routinely tip double that in a restaurant, come on.
I really REALLY want more people in experimental building - but there is a definite gap between "Kumbaya" and reality. For most of us, that gap is TIME. When I started building my first plane, I had absolutely zero business being in the "plane owner" or even "plane builder" club - but I knew that someday, somehow, I was going to get there. I paid cash as I went, when I could, if I could - and I waited when I couldn't. I bought a used, rebuilt engine. I bought second-hand avionics. I bought used tools. I had a solid 5-yr plan that only took 8 years. I never gave up. I never doubted that I could pull it off - only the timeline.
I don't remember who the quote is attributed to, but "If you think you CAN do a thing, or you think you CANNOT do a thing, you are probably right."