Quick question - do you have Emerald Club status?

If you don't and you just want a plane Jane midsize, look at Alamo as well as National. For a midsize you'll have access to the same core fleet, albeit supposedly higher mileage examples. However my last Alamo rental was brand new with only 9 miles on the clock.

From the UK, compare Kayak.co.uk and carrentals.co.uk ... if you're a member of Quidco, prioritise carrentals.co.uk because they offer cashback (usually 6-8%) on all bookings.

Although they may not be the cheapest, Auto Europe currently have a zero excess package on Alamo rentals in the US. Handy because it negates the need for any excess insurance.

A quick check of Kayak suggests National may still be the cheapest, so if you want to use the EA/ES ignore above re: Alamo.