Cyndi,
I think you answered your own question. A character breakfast is a great way for a young boy to have a memorable, unforgettable experience. Here are my suggestions for two of the better, and more affordable options.
Some character meals can be a bit pricey. But for a 5 year old boy there are still good choices.
Chef Mickey's in the Contemporary is a bit more expensive (the last time I went there it was $30 for adults, $15 for children, though prices can change) . Not cheap, but compared to many meals at Walt Disney World it is still on the very affordable side. The food is exceptionally good, and the buffet setting let's you pick from a lot of different items.
A more affordable and equally exciting experience is
Donald's Safari Breakfast. My lat time there it was $19 per adult, $11 per child (though again, prices change so call to be sure), and the African Safari theme was both fun and exotic.
In both your son will get to meet several of the lead Disney characters like Mickey, Donald, Pluto, Goofy, etc., and they will make it a truly memorable occasion.
Have a magical vacation!