After all bills etc, we have around £350 per month for groceries, travel expenses, DH's lunches for work etc. There's me, DH and 18 month old DS living on this. It is manageable, and we still have the occasional treat eg meal out, but this is usually only once or twice a month. It does mean being incredibly organised with shopping, eg meal planning, not being tempted at the supermarket to buy things we don't really need etc.
As I'm a SAHM I shop around rather than just going to the supermarket and I've really noticed a difference, we now get all meat from the butchers as its cheaper and nicer, I try to go to Farmfoods for bread and milk rather than the Spar even though it's closer, as 4 pints of milk is 85p at Farmfoods, £1.25 at the Spar. We get through one of them every day or 2, so it really does add up over the month.
Oh, and out of the £350 a month, we put £75 into savings each month. This pays for things like Christmas, birthdays, and unexpected expenses eg new tyres for the car when needed. Christmas and birthdays usually have a budget of around £50 each for me and DH, £40 for our parents, DS it depends on what we want to get for him but he gets one main gift, and a few extras. Not piles of things but he's spoilt by his grandparents anyway, and is too young yet really to care.
It can be annoying at times to not have much spare cash, have to plan ahead if we want to do something special as have to try and save the money from somewhere else to pay for it. For us it's worth it though, me and DH both feel strongly that me staying at home is the right thing for our family. So long as you and DH are BOTH happy then it's manageable, if the house is worth sacrificing other things for then absolutely go for it! :)