Big Thunder, Country Bears and Splash will probably be covered in New Frontierland's $400 to 500 million budget. One new attraction, even an E-ticket shouldn't cost that much.
I could see $350 million being spread around the non-Frontierland/POTC attractions to get everything else up to par for the 50th. But I imagine Space Mountain, Peter Pan and CoP are the three that need refurbs the most. Pooh, HM and IASW could use enhancements, but it's not urgent.
Lengthy refurbs for Pooh, HM and IASW
Update for HoP for 2016/2017.
Complete revamp of Space Mt
Complete revamp of PPF (includes increased hourly capacity... even if it's by a small amount)
Revamp for the Speedway if we have to keep it
Update of CoP
If it meant fixing up most of MK, I'd be okay with postponing Stitch/Laugh Floor replacements. And I would think any parade or fireworks show would get their own separate budget closer to the 50th (2018/2019).
Glad to hear TDO might actually increase MK's attraction count for once. Not just repurpose an existing area.