What are you planning on doing once you're in Wales? If you're going through the process described then sticking to your very small crowd, who are then going to take a test/isolate after you leave, and remain outside in fresh air the risk to other people is going to be much smaller compared to spreading yourself between a large number of people and going inside when the risk would be greater.

You've described being able to buy yourself out of quarantine as stupid mind. I'd much prefer you to follow the rules of the local country but recognise it's very difficult sometimes.