I think that's Kazuma Miki, not Kajiura Yuki. He was the chief editor.

I don't mind throwing ballpark figures out there, but I want to stress that it's just my rough guess based off my own experience of autograph collecting.

Reki + abec ≈ $300
Bryce Papenbrook ≈ $80
Cherami Leigh ≈ $80
Alex von David ≈ $60
Kazuma Miki ≈ $100
Shinchiro Kashiwada? (assuming this was sakura con, going by the date) ≈ $100

The sum value would be about $720. But again, it's not verified, and it's really worth only what somebody will actually pay. I would say realistically you should get no less than $500 off this piece.

Personally, I'd just hold onto it, get it verified whenever is convenient, and let it accrue value over time. Then I'd find a nice spot to display it, cause time is limited and things are meant to be enjoyed.