Quick service Theme park food average $15 per adult meal and $8 per child plus sales tax(I think sales tax is 6%). No idea about eating outside of theme parks. Merchandise is expensive, however, you can pick up stuff cheaper at Orlando Premium Outlets as Disney and Universal have stores there.
One tip, which is not for everyone is I also pack a few Disney bits from Primark, pound shop etc to give to the kids as new while there. Things like Minnie mouse ears you can get for £3 from Primark($25 at Disney), colouring stuff from the pound shop, Primark even have Mickey cuddle toys which are much cheaper than Disney world ones. They still get $100 to spend but that doesn't go far.