It does depend on individuals. For us, we are two adults and two little ones (age 5 and 3). We like to eat one nice three course table service with wine a day and then some snacks. We buy expensive type souvenirs (watches, collectables, adult clothes) and some pins.
As a result we budget about £150 per day and come back with change usually. But we are very regular visitors to Disney parks around the globe, so we do not buy that many souvenirs unless it's something really special (about to embark on my 50th trip!!!)