The daily rewards in HP are shown on https://www.eztk.net/witnesses.php?id=someguy123

You can put the numbers into https://value.steem.network and times the USD amount by 28 to figure out how much a witness makes per month.

Currently:

• Rank 1 to 20 get 340 HP per day = $201 USD per day / $5,600 per month
• Rank 30 gets 54 HP per day = $32 USD per day / $896 per month
• Rank 40 gets 27 HP per day = $16 USD per day / $448 per month
• Rank 50 gets 15 HP per day = $9 USD per day / $252 per month
• Rank 60 gets 10 HP per day = $6 USD per day / $168 per month
• Rank 70 gets 7 HP per day = $4 per day / $112 per month
• Rank 80 gets 5 HP per day = $3 per day / $84 per month

At https://www.privex.io - the cheapest witness server we have is $30/mo - so you could break even at around rank 100 with our cheapest server, and at rank 60 with a decent sized 64GB RAM dedicated server.

Of course the Hive price is very high at the moment, so the profitability of each witness rank could lower dramatically if/when the Hive price drops.