Look into Helium mining. Low entry cost, decently quick ROI so long as you can connect with other Helium hotspots. You could also try to get a Mini Doge miner. Also low cost of entry, but I'm not convinced it's a good investment. Finally, try Unmineable or Nicehash. You might be able to mine something with your GPU or CPU even if it's a little old. The last option would be your lowest cost of entry, and so long as you produce more than how much electricity you use then you'll have profit.
Not financial advice
Look into Helium mining. Low entry cost, decently quick ROI so long as you can connect with other Helium hotspots. You could also try to get a Mini Doge miner. Also low cost of entry, but I'm not convinced it's a good investment. Finally, try Unmineable or Nicehash. You might be able to mine something with your GPU or CPU even if it's a little old. The last option would be your lowest cost of entry, and so long as you produce more than how much electricity you use then you'll have profit.