Dijon mustard is to yellow mustard as a Rolls Royce is to your Honda.
A 454 gram bottle sells for $6.99, and that is 5¢ per serving. I don't mustard up both slices of my sandwich bread, so your mileage may vary.
Ketchup isn't often used on sandwiches, but if it were, a 17 gram serving would cost 6¢, assuming you bought a 36 ounce bottle for $3.59
Ok. Mayonnaise and mustard are the cheapest parts of the sandwich. You aren't going to save much money by going without a condiment, but some sandwich lovers prefer them bareback.
Kraft singles are a very inexpensive source of processed "cheese", mostly because they are wafer-thin. Twenty-four slices cost $2.54, or 10.5¢ per slice. It seems a little odd that the cheese might be cheaper than your bread.
I'll measure some real cheese a little later.
Iceberg lettuce is cheap, but a challenge to estimate more accurately than that. I used 14 and a half grams of lettuce on my sample sandwich, which is one 47th of a head of lettuce by weight (2¢).
But not every leaf of the lettuce head is suitable for sandwiches.
I'd guess that 60% of the lettuce wouldn't make it into sandwiches at all, raising the per sandwich lettuce price to 5¢
Adding tomatoes to a sandwich turned out to be surprisingly expensive.
33.8 grams at $2.99 per pound makes for a 22¢ serving.
Substituting ketchup is still a bad idea.
Finally, some processed sandwich meat. This Oscar Mayer Turkey was $2.99 for 16 slices or 18.5¢ cents per slice.
Oscar Mayer Beef bologna was a little more, $3.84 per pound or 24¢ per slice.
And there you are! Bread + Mayo + Mustard + Cheese + Lettuce + Tomato + Turkey + Mayo + Bread = Sandwich and sandwiches cost 95¢!
Processed meat and cheese is generally cheaper than deli meat and cheese. One of my favorite sandwich meats is roast beef, but it is expensive at about $8.99 per pound.
For example this 1.7 ounce serving (56 grams) of roast beef was 99¢.
Real cheddar cheese blocks are available at about $2.45 per pound. That's 12½¢ for three long slices (23 grams)
Processed turkey from a "Turkey Variety Pack" was $3.50 for 12 or 29¢ a slice.
Sliced salami is was $5.29 per pound or 21¢ for three slices.
$4.69 bacon works out to 58½¢ for two slices.
$1.25 avocados are each good split between four sandwiches: 31¢ each.