We stayed onsite (all star resort) last year. It was alright, but definitely small and cramped with no amenities (no internet unless you pay per day, mini fridge costs $10/day, etc). We got a great deal on a package though (hotel and tickets) so I can't complain.
We leave on Friday to go again. This time we are staying at a hotel off site (Quality Suites). Free high speed wireless internet (any hotel we stay at has to have internet because I still have school work to do on vacation and dp still has to check his work while on vacation), a small kitchen in each room, a semi-separate bedroom (with 2 queen beds), free breakfast every morning, outdoor pool and (the most important for us)- no pets or smoking allowed (lots of allergies here so it's hard to find a hotel we can stay at!). I think it was about $80/night. I think it's only like 2 miles away from disney world and we drive so will have our car anyway.
Our tickets were the most expensive part of our trip, we got them through AAA .
We eat breakfast in the hotel, head to the park for the morning, come back for lunch (also eaten in the hotel), go swimming and relax. Then in the afternoon (when it's not so hot) we go back to the park. We usually bring some snacks too. We sometimes eat dinner at the park or at downtown disney or somewhere (but dinner is usually eaten out somewhere... we are on vacation and want to enjoy it!).
We didn't really do many souvenirs. When we went to the walmart to stock up on food for the week we let ds pick a couple of the little stuffed characters (way cheaper than getting them in the parks!). We also went to a little discount shop and got ds a t-shirt for a couple dollars.
For gas (driving from kentucky to disneyworld), hotel(s) (we stay overnight at a hotel in Georgia on the way to florida and on the way back so it's 3 different hotels for the vacation for a total of 9 nights), park tickets (7 days, 3 people), parking (if you stay on-site parking is free, if you don't then you pay parking every day), food, souvenirs, etc.... for everything we will spend related to the vacation it will be less than $2000. That's not bad in Disney terms