Hi Heather
You are using FIFO (or LIFO) costing, and you probably shouldn't be. But even if you should be, the purpose of using FIFO is not to track different costs from different vendors - that is done directly in PurchaseOrders (or you can do it in Inventory using GridView). FIFO is solely used to "manipulate" financial statements, and only is important for companies that have slow turnover and wildly varying costs. For example, you buy a widget for $10 and then before it sells you buy another one for $50. When you do sell one, FIFO would send $10 as the cost of sales to your financial statements, Moving Average would send $30.
FIFO adds a much greater level of complexity to managing inventory versus Moving Average, and almost always results in an insignificant difference in your financial statements.
So you should change your costing method to Moving Average, stop fretting about lots, and track the cost of the same item from different vendors in PurchaseOrders itself.
If it matters so much which vendor's item you are selling to a customer (because the customer can tell the difference), then they need to be assigned different item codes.
Steve