That would put your weekly rate at $42.86 per day and your 10 day rate at $50 a day.... not much difference in the daily rate, but the total for 10 days sure seems higher ( keeping in mind that all the taxes and fees are spread over 10 days as well). I'm not sure what coupon book mentioned a 10 day rate, so I'm sorry I can't address that issue for you. But I'll try and give you some help here!

The general rule of thumb for a lowest daily rate is for weekend rentals. The most you can stretch a weekend rental is 5 days, if you pick up on a Thursday afternoon and return on a Monday late afternoon or evening.

I decided to check this rule of thumb. I didn't know your dates,times and location preference, so I made it up... keep this in mind, as pricing and availability are dependant on these factors and can change from minute to minute!!

I also decided to use a booking engine (Travelocity) so I could easily compare multiple car rental companies with one search.

This is the engine I used to search:

Find the Best Car Rental Rates in Top Destinations

(I also recommend checking the individual car rental company websites, after you've narrowed down your search)

I checked: (using a compact car for each search)

full 10 days -- August 5th - Aug 15th (Denver Airport) 12 noon pick up and return

7 days -- Aug 5th - Aug 12th (Denver Airport) 12 noon pick up and return

5 days (weekday) -- Aug 5th - Aug 10th (Denver Arpt) 12 noon pick up and return

5 days (weekend) -- (thu) Aug 6th - (mon) Aug 10th (Denver Arpt) 12 noon pick up and 6pm return

The best pricing for the full 10 days was through Thrifty or Dollar

The best pricing for 7 days was through EZ Rent a Car

The best pricing for 5 days (weekday) was with Payless Car Rental

The best Pricing for 5 days (weekend) was through Thrifty or Dollar

Bottom line... according to my check, your lowest daily rate, and your lowest total rate, is for a 5 day weekend rental (Thursday morning through Monday evening).