Price lists
Add the yards you buy from, with their phone number and a Price list: for each item, its price, its pack size and the date. New fences take the prices of the Preferred supplier. On each line, a price typed on this fence comes first, then the supplier's price list, then your default values.
Compare
On Materials, the Supplier line changes the supplier of a fence, and Compare suppliers appears once two suppliers price its lines: line by line, the cheapest in bold. The quote names the supplier and the date of its prices; the phone button calls the yard.