Rotax 915iS is 186.5 pounds
O-200 is 190 lbs
3.5 lbs of ballast and it seems like a doable option.
$35-38K Rotax new
3 gph at 100 knots so I'd bet faster at 5.3 GPH
https://generalaviationnews.com/2019/03/04/rotaxs-powerful-new-915is/
$70k for an O-320 new assuming new
Best economy 5.3 GPH at...