Wow that's a big request and I'd still need more information to be more specific. What kind of places do you want to eat? Here's some info that could help you in your planning. Universal has an offer on theri website which seems to be the best deal. Buy the 5 day park hopper ticket for less than the price of two single tickets. They run 95.80 per adult and 81.95 for kids. These do expire, the web site will provide you with the details.
Check out Mousesaves for the best prices in hopper tickets for WDW. The nice thing about these is that they do not expire, even the plus features for water parks, etc. are good until you have the opportunity to use them.
Food and souvineers create a huge gap. See you could be really frugal and give the child a set amount and bring some filler items (clearence items from the
disney store, dollar store,
walmart, etc) or you could give a rather unlimited amount here. Personally I have the kids save up their allowance for the year and that is what they have to spend. If there is little time to save between trips I will match what they are able to save.
Food--what are you planning on here--sit downs, buffetts, counter service? Sit down places have kids menus and are usually 8.99 or under for the complete meal. Adults average 25-35 each. Breakfast Buffets are around 9.99 per child and 17.99 per adult some are less. Lunch Buffets are 19.99 per adult and 9.99 per child again some are less. Dinner buffets aare 23.95 for adults and 9.99 per child. Plan on tax and tip as well. Dinner shows are 49.01for adults and 24.95 for children (unless they have gone up again). Two can have counter service for about $15-20 depending on what you order or if you are sharing (hot dogs, fries, drink and brownie at Casey's for example will only be about 10 per person. Since you are not staying on site you may want to try some places off site to eat as well to save money.
Bottom line, you need to decide what and where and budget form there.
www.wdwig has a great set of menus to check offerings and prices. Overall I spend about $100 per day on a family of four--2 adults 2 kids under 12. We sometimes go over the 100 other days we are under so it all averages out. We also usually eat breakfast int eh room--cold cereal and fruit/granola bars, etc.