Ignore the haters, it's MN, some posters only like posts where people are surviving on 17p a week. Yes, we get it, some people are currently dying without medicine or food in a bombed hospital in a country destroyed by war.
OP, I think you are looking at it the wrong way: abroad can mean anywhere and anything, did you mean a beach holiday? I found that UK holidays are more expensive than a cheap package one when I compare websites and the cheap package.
Your cost will be the travel presumably: you could drive, take a train, or look a cheap flights mid-week, or at times that are not that great. We are not far from France, and even Spain or Italy. There are plenty of campsites on the continent - if you avoid the fashionable places, you can find very decent holidays there for example.
A town and a rental with a view over a lake will be cheaper than a sea view villa too. Mainland europe has the equivalent of our Premier Inn, it's not too difficult to travel on the cheap, and only stay in a nicer air B&B for a few nights for example.
Enjoy your UK stay, if you have planned all your days in case of heavy rain, you are prepared for the worst, and will be pleasantly surprised if the weather is better.