I think it depends where and when you go both in the UK and overseas, and also want you want out of a holiday, so it's difficult to make a direct comparison in terms of cost. Holidays everywhere seem more expensive to me these days.
We don't have children so never plan to holiday anywhere during school holidays, not just because it's more expensive but because it's so much busier. I know many people don't have that choice.
I' think I'm unusual in that I'm not that fussed about a beache (or pool) holiday, although we discovered Northumberland earlier this year and it's a stunning coastline. There are lots of beautiful places in the UK the problem is the traffic and the popular places get rammed.
We are just back from another French road trip and it never ceases to amaze us how much space there is over there. It has it all ....cities, countryside, mountains, lakes, beaches.....and easy driving. Probably on a par costwise as the UK but without sitting on a motorway car park for part of the holiday. Well not until we get off the ferry in the UK

I love the ferry. You can sit in the bar or communal areas or disappear to the peace and quiet of your own cabin. But again the prices of ferries have shot up, like everything else.
We've travelled all over the world and I used to really love flying but now the whole airport experience puts me off. I hate being treated like cattle. Plus a seemingly "cheap flight" becomes less cheap once you factor in paying for luggage, an allocated seat, airport car parking, transfers the other side etc etc. Im not saying I wont fly, I just don't enjoy it like I used to and its always more expensive than it initially appears.
Anyway, wherever you all end up I hope you get a good deal, have safe travels and have a great time doing whatever you enjoy X