Change vendor and price on an item id

We are implementing Maintenance Management and our Dept of Transportation stated that they have items that they need to be able to order from multiple vendors (basically whoever is the closest and has the item they need) and so we need the flexibility to be able to change the vendor and update the price on an item ID at any time on a requisition. The item ID's are sometimes on contract with a different supplier than the one they are ordering from at the time. How can we set this up for our items to accept any supplier ID and