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Many-to-Many

I'm assuming you mean products that your organization is purchasing from a vendor?
Normally, we assign a product number to any product we are purchasing. If we are reselling, it makes sense to keep this number the same as our selling side. This may or may not be the vendor's part number, depending on how unique it is. Also, the manufacture's number may yet be another number that goes in this table. Normally I would suggest a "code" scheme that suits your organization, to avoid duplicates from vendors. Note, this number doesn't need to be an Access auto number. You will add a code as a field that means something to you.

Then you will have a table of vendors. You may purchase that product from many different vendors, each possibly having a different part number from the manufactures number if they are an intermediary. Now create a many-to-many table for product and vendor.

Pricing can get very exotic, especially on the sales side. I've seen very elaborate schemas to allow for all kinds of different pricing based on the customer, promotions, quantity, product class, etc. You may want to use this kind of exoticness in an elaborate purchasing system, one that mirrors what the vendors may have to find the best price and vendor.

When you do the actual purchase form, based on a purchase voucher and purchasing doing their diligence with specs, availability, price, etc. then you will use the suggested price or overwrite it, entering the quantity as well as the product number. Again, a many-to-many table for the purchase order form. I wouldn't consider it "bloating" as long as you are using foreign keys. I can't think of any other way to do it, since each line-item and order are unique.