I am from the UK also, and arranged a hire from Toronto, but using the car into the US.
I used Avis. I used the website to get an idea of prices, then use the 'store locator' (or similar) to find a branch near my hotel. I then call the guy directly, and found him incredibly easy to deal with. I believe many of these offices are franchised, and the owners often manage and work long hours in the office.
Give it a try!!