Vendor Group Agreement

Hello and can anyone offer some advice

I have the requirement to handle a group agreement which would be valid for a large number of vendors, that to say for each vendor belonging to this group we are able to use the same purchasing price. I don't want to maintain a purchase info record for each vendor, just one that can be used for any purchase orders that are sent to one of these group vendors. I have played with the partner roles in a purchase order but I do not think that it is possible to determine a price from a partner role without some development.

Advice on user exits BAPI and experiences welcome.

Steve