I know you say money is tight, but a trempoline is great. Lets off lots of energy and really fantastic for energetic boys.
Find out about parks locally, a short bus rides away. Festivals, free activities, etc. Do a schedule of things to do with one activity each day (swimming pool? you can get vouchers for free online if you search). Long walks, play football in the park. As I said, schedule one thing a day morning or afternoon and for the other half, go for walks/park.
When we are bored we bake fairy cakes and sell them to neighbours/people who walk in front of our house, for 50 pence each, then I take my boys to a sweetshop or they keep the money to buy a small toy and they really enjoy it! It's a bit crazy I know...
We have movie/popcorn/pizza every Friday afternoon. At weekends they help me make pancakes. It takes an hour just to get the mixture together, cut the fruit, etc and cook the pancakes, they love it, they can flip the pancakes.