Have you thought about doing it all yourself in terms of flights and accommodation.
As long as you are not travelling over a bank holiday or over half term week in May you may be able to get a good deal on flights, especially if you are willing to have an indirect flight (assuming you have no kids).
For Disney accommodation I would definitely look at booking directly with Disney or via a
Travel Agent that is a Disney specialist (
Dreams Unlimited who sponsor these boards are brilliant, I recommend Penny or Merrie). If you are going back in Dec then why not get an Annual Pass for 1 (or both) of you. Although having a Disney AP doesn't guarantee a room discount it seems that people usually do get one, especially in non peak times which early May would be.
For instance at the All Star resorts a room only would be $110 (approx) per night inc tax. If you were a member of the AA you might get about 10% off that but I guess if you don't drive that is not an option! The AP discount for May has not yet been announced but to give you an idea the discount for the All Star resorts for Jan (which is value season) is about $35 off per night.
Also remember if you do stay onsite then you can book Disneys Magical Express which will give you free transport to and from the airport.
Of course you can get some great bargains if staying offsite I just wanted to say that getting a package isn't always the cheapest option, especially if you have set your heart on staying onsite.
Nicola
PS good luck with the planning