virtuemart several price list

I have a client that need several price list for a single product and group shop so we need to modify virtuemart to allow have not only one price for product but 5 prices and when the user login , depend of the user group (5 groups ) , it select the price to show example group silver product 1 price $20 product 2 price $30 group gold product 1 price $10 product 2 price $20 because the way they have to calculate the price does not depend of a percent of the default price but the commercial criteria