Mark,
An off the shelf Aixro Wankel engine with a thingap motorgenerator ought to be the lightest custom option at ~50# today
Aixro, 33kW, 35#, ~$5000, http://www.woelfle-engineering.com/Prod ... ne_en.html
Thingap TG13360, 20kW, <10#, thingap.com; in Ventura, CA for two decades; would be hard to imagine it being more than $10,000, they have to be asked for pricing (though their 60kW motor seems to be worth $25,000!)
Then a suitable sized onboard rectifier+battery charger is all we need, that'll be (quite) a few grand. brusa might be close.
Some savings with less half the battery pack in $s, ~30# lighter than the eGull, with a 4-5hr range. There'll still be noise from the wankel to deal with.
Engiro RE20-2, 20kW, 70# with the same Wankel engine is still unavailable for private buyers.
Hope Oshkosh went great!
rc