Hi Maureen! Thanks for the question! You will need a valid theme park ticket to enter Epcot, even if it's just for dinner. Your best option would be to add a Park Hopper to your theme park ticket. For a single day, adult ticket, the current cost is $34 plus taxes. Note that this price can change at any time.
Another option is to change your dinner plans. There are several choices inside the Magic Kingdom, including the beautiful
Be Our Guest restaurant in the new Fantasyland or, my daughter's favourite
Crystal Palace, which is a character buffet featuring Pooh, Tigger and their pals. You could also hop on the monorail and
dine in one of the monorail resorts, either the Contemporary, Polynesian or Grand Floridian. So many choices!
Hope this helps Maureen! Write back with any other questions!