Here's a little 45 I built and sold in the late 1980s. Stock rear fender with the flap welded on, chrome heads, 21 in wheel, drag bars, dog bones, sprung solo seat, stock springer and a bates head light. This was typical of bikes you could build on the cheap back then. I remember the standard price for a 45 frame for many years was $150, 45 Springer $100 to $150, tanks $75 to $100, etc.
45 motors and tranny's were dirt cheap too! There were NOS parts in cosmoline everywhere. I still have NOS cylinders in the U.S. Government boxes left over. They came with pistons and valves. The "problem" is these '45 motors run forever and hardly ever wear out! If they do you just go a little oversize and throw a piston in it.
I have had the same trike since I was a kid and it just keeps going. It was smoking real bad out of the rear cylinder 25 years ago so I popped off the jug, pulled out the standard piston ran a hone through it and put a 5 over piston in it. I haven't touched it since and I ride it all the time to this day!
These little Flatheads are indestructible!