We don't need to use avgas, the compression ratio is so low (about 5.5:1) we could likely run Coleman fuel, and regular bronze grade has far more octane rating than we'll ever need. However we cannot run any ethanol. Ours has bronze trainer heads. If we are stuck fueling at the airport we run 100LL which up here is, if I recall correctly is about $1.65/litre (I hate looking at the gas receipts, it hurts). Our preferred fuel is ethanol-free regular, which a few gas stations carry for agricultural use.
We also have a 1C engine (6:1, aluminum heads, a few more hp) in the wings with only 11 hours since its last rebuild - it was either in, or a spare for, one of the faux-Rumpler biplanes in Lawrence of Arabia, so there is some interesting history behind it (documented, we have the docs from Slingsby). If you watch the movie, about 30 minutes in you'll see a biplane sounding and looking very tiger Moth-ish make a strafing run.
http://www.goldenageair.org/collecti...umpler_c_v.htm