No, it wouldn't be that much higher for mogas (typically a 91-ish octane unleaded, E0 (ethanol-free) gasoline).

If there were an unleaded 100-ish octane fuel legally available as a substitute, that would have demand if 100LL were banned. Over 70% of the avgas burned is burned in airplanes that are not eligible for the STC* to allow them to burn mogas (typically as a result of having lower worst-case detonation margins as a result of being turbo-charged, super-charged, high-compression, or some combination).

* - Supplemental Type Certificate - an airplane modification, in this case a mostly [entirely for most airframes] paperwork modification, to their original type certificate.