EA's charging here is priced at $0.44 per minute, so with that budget you can charge for 3.70 minutes.
Assume it spends that whole time at 80 kW. This is probably optimistic, it will take time to ramp up to that. But we'll forget about that, and assume the car starts from near empty because the Solterra's charging curve is trash and will begin throttling the speed down when it's about 35% charged.
3.7 minutes at 80 kW gives us 4.93 kW of charge. EPA rates the vehicle at 3.23 miles/kW, so for the equivalent price of 20 miles of gas we've added... drumroll
15.9 miles of charge.
With other vehicles or in an area with different gas/charging pricing, your mileage my vary. And if you look at a straight ICE competitor of the same size as the Solterra as the MPG reference it will be worse than 35 MPG (requiring more gas and giving you a higher charging budget), so basing this on my smaller car did limit that. But regardless, fuel price isn't necessarily a huge advantage for a rental EV.
If I were talking price for L2 charging at home in my garage then I'm sure the EV would be way cheaper, but that's now how anyone will be using a rental.