I believe that American Flyer was a DP Harris’ Rollfast badge for that HP Snyder-built sport-motorbike of the later 1930’s+.
General advice may be to try to acquire a bike as complete as possible, as building-up from a bare frame may have negative return on investment.
If the project is just for the enjoyment, then the question may be more about supply and demand, and how much patience, or how long the buyer is willing to wait?
Another consideration is the shipping cost for a frame. For example, if shipping is $100, might a seller expect $85 for the frame, (or vice versa), for a net $185?
An American Flyer head badge might also fit on various other Snyder-built frames?
*When some people hear American Flyer, they might think of Louisville bikes made by that other manufacturer.
Sounds like a neat project!