YNAB is £29.99 from the Steam Store, but Steam have sales every so often where it can drop to as low as £7.49. You can set an alert for when it's on sale.
You can install it and try it, fully functional, for 34 days by downloading it here. That's enough to do a whole month plus set up.
It really is so easy to use - totally customisable to have as many or as few categories as you want, with as many budgets as you want and as many accounts as you want, with as many computers/tablets/smart phones as you want.
Star, you could even have DS have his own budget with pocket money, for instance.
It can sync across multiple devices, using drop box, so if your DH works in an office, for instance, he could view and adjust the budget there, and you could do so at home, and it will sync the versions.
It's an envelope budgeting system, so it's very practical - if you have £100 and you want to spend £80 on minecraft, you put the £80 in the minecraft 'envelope'. That only leaves you £20 to share between all your other 'envelopes'.