That's up to you. If you call it a schedule C business, then you pay $20 to mine a $200 coin. That gives you $200 of gross income, $180 of profit. You pay self employment tax of 15% ($27) and you pay income tax of between 10% and 33% depending on your other income. Let's say 25% for most middle class taxpayers -- single earning $40K per year or more -- so that's another $45. At the end of the day you cleared $108 from your $200 coin. (And you'll owe some state tax depending on your state.)
Now, this is the same position as a painter or photographer or other artist or craftsperson. You pay $20 for materials, sell the work for $200, and net $108 or so after taxes and expenses. You have to decide whether making an after-tax profit of $108 per coin is worth the trouble.
If you don't report it as a business but just as a short term investment (bought for $0, sold for $200) then you can't deduct your mining expenses, but you don't pay self employment tax. So you pay a straight 25% on the $200 profit ($50). After subtracting your $20 cost, you net $130 per coin.
(If your expenses were higher, you might pay less tax as a business, but if your expenses are 10% of your selling price, you pay less tax using the investment rules.)
Everyone in business looks at their taxes and makes the same calculation, is it worth it?
