Marketplace with price regulations by admin

Hi there.

I am looking for a Marketplace solution where the Vendor can create a product etc. but the price is set do a fix price defined by the admin.

here would be the usescase
1. vendor signs up
2. vendor gets approved by admin
3. vendor creates a product, description etc.
4. vendor cannot enter price field, it would be predefined by admin e.g. 20$
5. products gets submitted and available in store.

so far i spent hours in searching for a plugin etc. with no luck.

cheers Pascal