Almost $700 for the 22cc and goes up from there. It looks like an interesting homebrew engine. However there are already some great engines out there that are allot more refined and suitable. Honda makes a 25cc with a 360 oil sump so it can be mounted upside down and it burns straight gas. They also make a 35cc that flys the 1/4 WWI warbirds like a dream. Total cost is about $300. Stihl makes a 65cc 4 stroke that performs about like a G62 and burns a 32:1 mix so it can also be mounted inverted. Purpose made doesn't mean better made or more suitable.