Depending on what dates you are staying and what
special promotions Disney is running, staying at the Royal Plaza and All-Star will cost about the same (but you will have to price this out!) It would cost more to stay at Animal Kingdom lodge, as this is a Deluxe Resort. I recently stayed at the Royal Plaza. It was nice, but I did miss the magic of a Disney Resort property.
One thing you will not get with staying at the Royal Plaza is the use of Disney's Magical Express, so you will have to factor in the extra cost of transportation from the airport. Also, you will not get to take advantage of the Extra Magic Hours at Royal Plaza.
If you are planning on driving, parking at the theme parks is $12 per day (subject to change) if you are not staying at a Disney Resort.
The Downtown Disney Resorts are in a great location and a nice choice if you decide to stay there. I personally did not find that it saved me any money, but we did have a nice stay.