MarketPress: Create Product with Variable Volume Pricing Options

I want to offer a variable pricing option based on volume. I figured this would need to be a custom plugin, but I was hoping for guidance on how to frame the requirements and on any available plugins that can be incorporated into the overall solution.

This is what I would like to do:

1. Seller creates a product and sets pricing based on different volumes. The form would allow the following data entry:

Field 1: Level 1 Price; Field 2: Quantity Need to trigger Level 1 price
Field 1: Level 2 Price; Field 2: Quantity Need to trigger Level 2price

2. Seller sets auction deadline for pricing.

3. Buyers click on "Buy Now" and confirms intention to bid.

4. Auction closes. All buyers who confirmed get charged price based on final quantity purchased collectively by all buyers.

Once I get a better handle of how to frame the requirements, I'll post a job for this.

Many thanks!