Obviously I can not really afford a gym, but I have an area out in my garage where I have started working out. To start with I got a nice big fan, because it would be too hot out there if you did not have that to cool you off. It is the sort of fan the guys in the shop use and as long as you stand in front of it you do need get overly hot. I found a web page with some adjustable dumbbells to buy and that saves a lot of space. The come with a little rack and the weight sits in the rack. Then you make the adjustment and it comes out of the rack with the amount of weight that you need to work out. The kids all use them, but of course I am not sure that the youngest ones need to start with weight training. You read a lot of different things about that and I do not know what is right and what is not. Some say they are old enough and others talk like you should wait until they are old enough to vote.
The big thing that I use is this old treadmill that I found at a yard sale. The guy who had it before said it was just too big and I figured the same thing. Of course I do not use the garage to park my truck. I have a Ford F 350 duallie, meaning that the back end of it is about exactly the same width as the entrance of the garage. I suppose you could probably get it in and out of there if you were determined to do it, but it would not be worth the effort to me. So the treadmill can have the parking space.