I saw a show called Extreme Cheapskates or something like that, about people who, for instance, spend an entire day raiding dumpsters or cycling around picking up loose change, because it's cheaper than shopping and it feels like free money. The problem, of course, is that your value assessment of these activities does not take into account your valuable time. Let's say you manage to pick up $7.50 in loose change around town, and it takes you 8 hours to do so (actual example). You are settling for a wage of less than $1 per hour. People would pay you more than that to rake up the leaves in their yards.
It's that level of cheapness where it starts to feel like you might have a mental illness similar to hoarders, placing an irrationally high value on something that actually costs you more.
Mokalus of Borg
PS - Calculating costs vs savings is important.
PPS - But, as a guideline, spending your whole day scrounging for less than minimum wage is not worth it.