"American Idol" is struggling to land judges to join Katy Perry because of budget limitations, but it still has a weapon on reserve to lure 'em in -- a partnership with Disney.

Our 'A.I.' sources tell us ... the show's talent budget has a $40 million cap, which has been depleted by signing Perry for $25 mil and Ryan Seacrest for just over $10 mil. So, producers are having to get creative and sweeten the deal by offering celebs Disney perks that will turn into a big payday.

We're told the perks include production deals, licensing and merchandising deals for Disney properties ... and also theme park partnerships. For example, Disney's Hollywood Studios features the Rock 'n' Roller Coaster Starring Aerosmith ... but can always add more names.

As we reported ... 'Idol' made an offer to country star Luke Bryan to be judge #2. As far as we know, the deal isn't sealed ... at least not yet.

Perhaps we'll be seeing Space Mountain starring Luke Bryan.