I miss the gym badly and I have zero equipment here at home.
I was in the same situation. Granted, I'm a tired old man, and not looking to build my body, but exercise is still necessary for good general health. I was a very fat mess most of my life, but saw the light and actually entered my 50's looking halfway decent-- I'd shed the weight (260 down to 180), and then had the upper body looking good. Unfortunately, I lost everything when I ruptured my bicep tendon (doing the housework, not in the gym), and had post-surgical complications, so the recovery went on for so long that I ended up fat with no arms again. It's not easy to grow it back (or loose the gut) as you get older (now pushing 60), so I decided I'm not about to loose such as I've gained back again. For a while I had some heavy landscaping projects to serve as a workout, but those are almost done, and it is going to be months before the gyms reopen here in California. But I had nothing at home, and was not about to pay $200+ bucks for a pair of dumbbells (incredible, but that's what they are going for on Ebay).
The sporting goods stores may sold out and closed, they gyms may be closed, but Home Depot and other building suppliers are sort of open. So, DIY cast concrete dumbbells it was, for under $20:
I used 3 lb plastic tubs that low fat cottage cheese comes in (I consume a lot, and the plastic tubs are useful, so I wash and save them) for molds. Even with the densest standard concrete mix, they only made a pair of 20 lb dumbbells, but that's a start. They are a little bulky, since the usual cast iron is much denser than the concrete, but still quite usable. I'm looking to find something denser than the usual pebbles to mix into the concrete, to get a heavier set in the same size. There is a steel pipe cast into the concrete ends as the handle, although at this weight, much cheaper PVC would have been strong enough to work (the steel pipe does add about a pound, though).
If you try this at home, note that it is necessary to anchor the pipe in place, not just stick it in the wet concrete, or the end may fly off. I drilled and threaded a couple of bolts in an X through the end of each pipe, as seen below at the red arrow. Obviously, you cast one end at a time, then flip everything over to do the other end.
Now I'm working on a barbell. Even with the concrete mix I have, I calculate that if I use the big jars that 5 lbs of protein powder comes in, filled with concrete, as the weights, with a pipe bar in the middle, I'll get about 100 lbs. That will have to do for bench press. I'll probably make another, a little lighter, for curls. Or, since the pipe is the most expensive part, maybe make the concrete weights interchangeable, like a real bar...