Every six months or so, I buy new walking shoes. We walk several times a week weather permitting from November through April (otherwise too hot!), so other than the shoes, that's free. When it's not nice out, I do weights, stretching, exercise bands and use our treadmill. Most of my weights are very old, though I got some new kettle bells for Christmas. I had mixed in some fairly new exercise bands with some that were definitely too old and had a couple of them snap. Then discovered I couldn't tell which were the old bands, so threw them all out and bought new.
In high summer, we go to the neighborhood pool and swim laps (slowly, we're not good, just persistent). You could call that free since we pay whether we use it or not.
The Landice treadmill was $4500 some 17 years ago, but is still going strong and has a lifetime warranty, someday I suppose we'll test that.
For entertainment while exercising, I watch NFL games during the season and record all the college football games I can find. In the NFL offseason, I watch the college games. Football is good for exercise entertainment as it doesn't require strict attention and I can always back up if something exciting happened.
With some imagination, you don't have to spend a ton of money.