I also used Enterprise earlier this year from Derry, they were kind enough to pick us up from the airport to take us to their office 2 miles away FOC, which was handy. They were the only major car rental company that would hire me a car - I've only held a full license since January
I was upgraded FOC from a Chevy Aveo to a nippy Seat Leon tdi. The only additional cost they offered was a £20 add on to reduce the damage excess from £600 to a max of £100, which I had no problem paying (it came off the £200 deposit when they returned it to my account).