We plan to rent a car in Cardiff, but then plan to to turn it in in north Wales - will the rental be subject to a large drop charge, like in the USA?
Last year I picked up a car at Heathrow & had it for about 10 days & dropped it in London & the drop charge was about £25.
I dropped one off at a different location this year and it was also about £ 25.
I have found it varies between car companies. You have some areas that may only be served by one or two companies which raises the likelihood of a higher drop charge. They usually aren't outrageous and it's part of the cost of doing all this touring stuff. Check your prices before you rent.