Dear 100 Hour Board,
How can I buy Music Concerts Tickets Online at the Cheapest Price?
Groupon often has good deals. Googling "cheap concert tickets" also directed me to goodseattickets.com, vividseats.com, ticketzoom.com, cheaptickets.com, tickpick.com, and stubhub.com. I can't vouch for any of these services other than Groupon, but you could check them out and you might get some good deals!
Alta named most of the websites I could think of above. Most of the time the prices will be more or less the same, and no single one of those websites is better than the other consistently, so it's best to compare each time. Sometimes buying directly from the concert location works because you aren't paying any third-party fees, except sometimes the online convenience fee (more like inconvenience fee...)
Other than that, you can often look on public sale websites for people who bought tickets and are trying to sell them secondhand. KSL Classifieds often has concert tickets, and I've also seen some on Facebook Marketplace. As usual, be careful about buying from people you don't know because there's a higher chance of being scammed this way. However, I have bought concert tickets for basically dirt cheap off other people last second, so it is possible.