How to make a one-time donation?

Yes, donate the value you want preferably at the beginning of the month and then cancel your subscription before the month ends.
You can also subscribe at $1/month.

As noted on Patreon:
If you are willing to make a donation at the end of the month, please note that you will be charged immediately for the current month and again for the next month at the 1st of the next month. I recommend delaying the donation until the 1st 0:00 (Pacific Time, UTC-8:00) in this case.