It looks like the upcoming Kingdom Hearts HD 2.8 Final Chapter Prologue will be priced higher when compared to the MSRP at launch for Kingdom Hearts HD 1.5 Remix and Kingdom Hearts HD 2.5 Remix. You can check out the price tag, and preorder the product if you want, for the 2.8 collection with this link.
For the uninformed, Kingdom Hearts HD 2.8 Final Chapter Prologue comes with the HD remastered port of Kingdom Hearts: Dream Drop Distance, which features Sora and Riku undergoing the Mark of Mastery exam in preparation for a new threat. The other part of the compilation is a movie called Kingdom Hearts Chi: Back Cover (movie), which will connect the story of the previous entries to the upcoming mobile game, Kingdom Hearts: Unchained Chi.
Perhaps the most interesting content is Kingdom Hearts 0.2 Birth By Sleep: A Fragmentory Passage. This completely new chapter will feature Aqua, connecting the events between Kingdom Hearts: Birth by Sleep to Kingdom Hearts 3.
Square Enix is expected to release Kingdom Hearts HD 2.8 Final Chapter Prologue sometime next year. The compilation is currently only announced for the PlayStation 4 even though Kingdom Hearts HD 1.5 Remix and Kingdom Hearts HD 2.5 Remix is only for the PS3 while the upcoming Kingdom Hearts 3 is coming to the Xbox One as well.