Look at some of the resorts in the Cancun/Maya Riviera area. Dominican Reuplic all-inclusinves are OK but the cheaper ones are not as nice as the Mexican ones, IMHO.
Check out
www.cancunmx.com for some good advice and deals in that area of Mexico.
Also look at
www.vacationstogo.com for ideas of places to go. They have a resort area that lists all-inclusives. Might give you some ideas and prices. Then try going directly to the resort website and see what they are offering. This may be when a travel agent can get you a better deal, upgrades, or other perks.
But remember that July 4 will might be considered a premium week in any place that markets to Americans.