@Danielle1323 I think your math is wrong? Let's assume 4 weeks is a month. The weekly rate is $100 and the monthly rate is $400. The weekly discount of 10% would mean $90 a week. Four weeks at $90 a week would be $360. The monthly discount of 20% would bring the $400 down to $320 for the month. I.e., four weeks of a 10% discount would not be a 40% discount - it would still be a 10% discount.
You can simply offer him a better monthly discount if that's what you'd like to do. Figure out what you'd need to cover your costs for the month, add something for profit and something for wear and tear, and go from there.
Once you've agreed, you could send hm a special offer (if that works - I can't remember if it always shows up), or ask him to withdraw the request so that you can re-set the monthly discount, then have him request again.