Mining will kill your GPU, yes, because it is running at 100% 24/7. Mining cards last about a year, depending on whether you overclock them or not. Also, you'd need a good card to make $100 mining, like an RX 570 or above. So yeah, in about 3 months you'd pay off the card, make another $900-1000 before it dies. Take $300, buy new card, repeat, and you've made about $700/yr. But you've also spent time on setting it all up, running it, maintenance, etc. So you have to calculate whether $700/yr. is worth it for all the work you'd be putting it. It's not for nothing that miners fill whole rooms with cards to get a decent return.
You're better off just selling weed to friends. Buy a half pound for $600, that's 8 ounces. Sell 7 ounces for $110-120 each, leave one for yourself to smoke and you're making $700-840 on each $600 investment, plus you smoke for free, plus people will think you're cool. Just sell to friends and their acquaintances, never to strangers, don't advertise on the street and don't carry any significant weight with you except when picking up. Don't do deals in front of your door, have the person come in, or better yet, you go to them. Always weigh out like 0.2-0.3 more on the scale and you will get return customers. All you need is like 10-12 regulars and you can make $200-300/mo. I mean, sky's the limit with drugs, but it's all an ambition/risk trade off and you probably don't want to have more than half a pound at a time. If you don't have plastic baggies, it's hard to nail you for selling, even if you have a scale, so if you're caught you claim it's all for personal use, you wanted a deal on the amount cause weed is expensive, etc. Give people weed in like ripped pieces of supermarket bags, or small jars, or something else, as long as it is not those drug bags, and you're good.