That cost saving might come back to bite you. Overused cutting oil loses its ability to cool and lubricate properly. I've seen it lead to faster tool wear and even cause tiny defects on finished parts that you only catch later. You might save on disposal now but spend way more on tools and scrapped work down the line.
Ugh, this is such a common mindset with everything now. People run their phone batteries to zero and skip oil changes to save a buck too. It always costs more to fix the damage later.