In terms of spending btc on a machine to the amount of btc you’ll get returned there are some good deals out there. For example I see every now and again second miners selling 90-95th S19 miners selling for under $500, or new 86th miners selling for $650. If you buy a 95th for $475 right now you’re spending 0.017 btc for a return of 0.028 btc in 3 years if you have 33% uptime and the default difficulty is 3.2% monthly for the calculator I use at https://smokinghopium.io/
Even if the average monthly difficulty was 7% you’d still be at break even and of course if you have enough solar credits and can run more outside of solar hours, obviously winter and summer varies which is why I said 33% uptime. Good opportunity to dabble and have some fun with low risk, and earn some interest on your btc 