Sadly though, this is, for the majority of the resident parents, the reality.
It is about budgeting well and trying to find the perfect job financially and for what works for your family.
With regards the costings, if you work out when he will be having the children, then any costs relating to the clubs or childcare needed on that day, should fall to him. So it maybe worth ensuring that say his midweek contact involves one of these.
The rest is, I'm afraid, yours to bear.
The reasons for not sharing costs 5050 is quite simple, it would be a nightmare. He'd say they don't need xyz or that you're choosing the most expensive abc and you'd constantly be having to prove and justify spending. As it stands now, you receive the child benefits and any associated benefits, plus the child maintenance to spend how you deem fit. Imagine if he could dictate that you live elsewhere in cheaper accommodation or how to spend your time with the children. It would be awful for your freedom to move on as you need to.
If you can make informal agreements with him, you may get more money, assuming of course that he pays! You can also have the discussion that you share significant other costs on top, such as school uniform etc. Though remembering that he isn't obligated with any of those additionals.
I'd also, advise you @Chocpie and any other lone parent who receives child maintenance, please don't rely on this for absolute survival as it can stop at any point or reduce without notice if he loses his job, gets a lower paid one, retires or goes self employed or if he moves in with someone with children and/or has additional children etc. There are so many, predominantly women, who do rely on this for the rent or mortgage and then have the rug taken from under them.