Discounts for monthly car rentals are hard to find!
The first thing I like to do is quickly compare multiple rental companies.
First I checked with a booking engine (Travelocity) so I could compare several companies at once. I checked SFO From Nov 20th at 12 noon to Jan 22 12 noon
According to that search, the cheapest was Budget.
This brought the rate down even more.
I know that Budget also offers a discount for seniors (renters over 55).I went directly to - Budget.com (opens in a new window) - and entered the generic senior rate code (I called in to a Budget res line to ask for the code) in the box that asks for the optional offer code (BCD)
and checked for a midsize for the same dates and times as a resident of Denmark, using a generic senior car rental discount code and got an even better rate.
I also wanted to check Avis, because I know that they used to have a long term rental discount coupon for $50 off monthly rentals
If that coupon is available, iit automatically puts in a car rental discount code and coupon # Avis also offers a senior discount as well. But even after checking those two options, Budget was still the cheapest rate that I could find.
Hope this helps!