Obviously it varies person to person. We managed to juggle our work hours and parents helped, so our childcare costs were very limited. Add in cloth nappies and we didn't find preschool too horrific at all.
However, now they're teens, the costs are horrific. Monthly costs alone for car, car insurance, petrol, hobbies are easily double what we ever paid on childcare. But we live rurally, so a car is almost a necessity. And that's before you consider the mobile phone contracts, cost of clothes, shoes, going out, pocket money, buying textbooks, school trips, tutors (if you do that sort of thing) and it soon mounts up!
However, it's horses for courses... if you had full time nursery fees to find, but live in a city where your children can get themselves around without driving lessons, car etc... you'd probably find pre school more expensive.