You don't need to spend that much for a maintainer. This is 1 amp, which is all that's required:
https://www.amazon.com/dp/B07W46BX31...NsaWNrPXRydWU=
You wouldn't want to use it to charge a dead battery, as it would take at least 3 days, but it provides more than enough juice to prevent the battery from discharging while the car's not being driven.