I'm not sure what the status is in regard to wholesale pricing in Marketpress - I've seen a few posts mention it but nothing concrete about whether it will appear in the future.
I've got a client who would need to enter a wholesale price against each product (similar to the way sale prices are handled).
This would need to work for product pricing and variant pricing.
The wholesale prices would be used for a logged in user, depending on user role, or a "wholesale customer" check box.
Essentially there would be one cart, just different price options at the product level.
Hopefully that makes sense?