I find that marginal costs/benefits for low-priced items are best contemplated multiplicatively, not additively. A $4-5 pint at the bar? Only a couple bucks of markup, but replaceable with 3-5 bottles of beer at home. Out to lunch for $6? that's 2 or 3 home-cooked dinners. 80-cent vending machine candy bar? only 30 cents more, but that's 60% more expensive than walking to the student store. The habit of thinking this way stretches pocket money multiplicatively.
I would think on any given night that most people without alcohol problems would prefer 1 pint of beer at a pub to 5 bottles at home. Same for a lunch out with friends vs 2-3 dinners home alone.
Your theory is obviously sound, but many times the "more expensive" (on a dollar per unit basis) item is even more valuable (on a hedon* per dollar basis)
Only because alcohol problems were mentioned: I drink one beer at a time (ok, sometimes two), so "5 bottles at home" is "5 nights at home that include a bottle of beer".
