I read this BBC News article the other day and my first, and lasting, impression was simply: if taking your kids out for the day costs £80 then you're doing it wrong!
Now I know that if you factor in travel and entry costs to a theme park or taking the family to the cinema with popcorn etc. then you might well be able to spend £80 on a day out but that doesn't mean you have to, or that all days out should be like that.
When I was growing up, my Mum (while Dad was at work) made sure my brother and I didn't just sit around the house or mope around the housing estate during the summer. We had lots of days out and I doubt that any of them came anywhere near to costing the equivalent of £80. On many of the days the only cost would have been transport, and that was taken care of with a Family Day Rover -- a relatively cheap ticket that was valid on all buses and trains within West Yorkshire for a single day. We took sandwiches and drinks with us (which weren't an extra cost as we would have eaten if we had been at home) and we explored the countryside, villages we had never been to before, and museums; many of which were free to enter (more and more museums seem not to charge an entry fee now, so this is an even wider choice than when I was a child). There were days when money was spent on tickets, ice creams or a sticky bun, but these were the exception making them all the more enjoyable and not something that was simply expected. There were also days when we went further afield; I remember one summer when Dad was off work, we all went to Scarborough for the day, but again we took lunch with us and played on the beach, no expensive entry tickets etc.
I guess my point is that claiming you can't afford £80 to give your kids a day out suggests to me that you are too lazy to think up an interesting day out and would rather pay for someone/something else to provide the entertainment. Jump on a bus and explore the countryside, it won't cost you £80 and maybe the whole family will get some fresh air and learn to enjoy both the outdoors and each others company.