One that you can't afford to lose.

are you just asking for the most expensive item in each slot?

There's no such a thing in my opinion, at least talking aabout getting the gear from AH.

does that include skins for each item?

OP's a timewaster - just ignore

8.3 mp headgear (no idea wich one is actually the most expensive since they are usually quite cheap. I will say Helmet of Valor just because)
8.3 mp robe of purity
8.3 mp tenacity shoes
8.3 mp satchel of insight
8.3 mp morgana cape
8.3 eel stews
8.1 inv potion maybe?
8.1 command mammoth (or maybe a recruiter one, the toad?)