I signed up for the gym today. It's somewhat expensive at 150€ a month roughly, but it was the one closest to home.
Spending an extra 1800€ a year would eat into about 15% of my annual contributions to my retirement fund.
So instead I decided to stop drinking coffee that costs money and only drink the office slop. I started doing this two months ago to see if I can manage and honestly it's pretty easy to do and sometimes I don't drink any coffee at all.

It evens out.