MarketPress eCommerce - Global Price Change?

I am looking to launch our ecommerce sites for customers.

I have had several requested features (one being single-page checkout - that's another thread) - but the one that seems most pressing to me now is that we need the ability to do global price updates for content that is coming from vendors.

Most of my customers are in the jewelry industry.

Situation:
We put 500 items on the client's website with pricing attached.

Vendor updates their pricing (due to gold and diamond valuation fluctuation) and send client a spreadsheet (or offer via API call).

Client wants to add their 2x markup on the item and have posted to the ecommerce site.

Is there a way to do a global update to pricing without doing an export, manually changing the CSV pricing, then reimporting?

What I'm thinking is a process whereby we could have a "markup" field that is applied to all 'pricing' and then has that price show on the website.

Also - in case we get this to a 'feature request' -- I'd like to be able to do a markup factor by tag -- so that if we tag products as 'vendor1' and 'vendor2' we can add a 2.0 markup to vendor1 and 1.5 markup to vendor2, etc.

Thanks in advance for the help.

Jeff