All SNES courses = 5 bucks
All N64 courses = 5 bucks
All GBA courses = 5 bucks
All GC courses = 5 bucks
All DS courses = 5 bucks
All Wii courses = 5 Bucks

Additional character pack (all chars like dry bones etc) = 5 bucks

200cc = 2 bucks.
250cc = 2 bucks

Something like that.

Ok
Characters - King Boo, Dry Bones, Funky and maybe Birdo or Petey
1 or 2 cups
Battle Mode courses (a must)

n64 battle courses

Cheese Land GBA with the same shortcut
Vespa Scooter - AE86 DLC promoted by Keiichi Tsuchiya/Initial D
Waluigi Flipper DS
Mii without helmets.
Track editor.

This, and the ability to configure rules and items to replicate N64 battle mode.

Seconded

Battle Arenas, new maps and remade maps based on the anti gravity feature.

- More characters added to Roster.
- More New or Old Tracks to race on.
- More Kart parts for customization.
- More weapons/items.
- DLC option that changes a track's timing setting between Day/Afternoon/Night.

Darn, that's a good one. N64 battle courses are my semi-favourite. Wii has better ones IMO.

Donkey Kong mineshaft cart