Pete,
Perhaps it might be a good idea to "weigh out your options"(pun intended).
I would suggest going to the post office with assorted mailers with various amounts of chips in them and get the prices for those packages.
Have a mailer with one chip,another with 2,another with 3 etc. Maybe up to 10 or so chips(depending on how many you seriously think will sell to the same buyer.
Now you will know exactly how many it takes before higher rates kick in and how much it will cost the buyer in postage and now you can then list the assorted prices in your listing.
So now you can list low and the postage is irrelevant.
I know that up here it costs us $2.00 to mail 1-3 chips and then the rate goes higher for 4-8 etc.,so I list those prices in my ad.
Simply take a bit of extra time and then your customers will always know what is happening(IN THEORY anyway ).