Believe me, this is such a great idea that I recently received exactly the same feedback.

It's already on my roadmap because the user indicated that it would be effective to demonstrate "what this skipped purchase could grow into in 5/10 years at X% compounding."

The concept would be: rather than merely saving $80 today, demonstrate that, at a 7% annual growth rate, it will reach $157 in ten years, making the "opportunity cost" even more difficult to overlook (and much more motivating if you're saving for things like a down payment).

You have no idea how much these suggestions are helping me shape the next wave of features, so please keep coming.