The absolute best gaming monitors are ones that are brimming with features like G-Sync or FreeSync support, HDR capabilities, ultra-high refresh rates, and other sometimes pricey amenities. If you want to just keep things cheap, though, have a look at AOC's 27-inch display (27B1H) that's on sale at Staples.
It's on sale for $109.99, down from its $199.99 list price. It doesn't usually sell for the full MSRP, but does routinely go for around $130, so you're saving a chunk of change right off the bat. Even better, if you enter coupon code 83042, it drops the price to just $94.99.
AOC 27" Monitor (27B1H) | IPS | $94.99 (save ~$55)
It's a mostly no-frills display, but it does sport an IPS screen (usually you find TN panels at this price) and is under $100 when you apply coupon code 83042 at checkout. That's a tantalizing price for a 27-inch monitor.
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The additional discount is what makes this an interesting deal. This is a fairly basic monitor with a 1920x1080 resolution, 60Hz refresh rate, and 250 nits brightness, but you're also paying a lot less than what you would for a decked out display. You're just not going to find a 27-inch monitor with G-Sync selling for less than $100.
AOC is quick to tout a three-sided 'frameless' design, though what's more noteworthy in my opinion is the panel type—it's an IPS screen. At this price, cheaper (and lower quality) TN screens are far more common. Typically, IPS screens offer better color accuracy and wider viewing angles (178 degrees) than TN displays.
This is not for everyone, though if you're pinching pennies, looking for a monitor for the kids, or need a secondary display, this is serviceable option.