This hot-swap mechanical keyboard is $39.99 at Amazon today
I've tested the RK61 and it's extremely good for the money.
Keyboard company Royal Kludge aren't doing themselves any favours with that name, but they do make some of the best cheap options on the market. Today their RK61 keyboard is down to $39.99 at Amazon US, a great price for a 60% keyboard with 2.4GHz wireless, Bluetooth and USB-C connectivity, hot-swappable switches and single colour backlighting.
I've tested out the RK61 for Eurogamer, where I ranked it as one of the best 60% keyboards on the market. That's thanks to a very agreeable asking price (as above), but also because it's a decently built keyboard that feels surprisingly good to type versus more expensive alternatives from mainstream brands.
This particular version comes with red MX-style switches, which are a light and linear mechanical switch that provide more feedback than non-mechanical keys but without noticeable tactile bump or audible click that you might be familiar with from other mechanical switches. This makes it a good choice for use in shared spaces, and is often recommended for gaming as the low actuation force makes it very easy to tap keys with a quickness.
As noted in the intro, you can swap out these switches later for something else if you prefer with any 3-pin or 5-pin MX-style switch. This opens up a lot of options for later customisation and can improve the feel of the keyboard substantially; of course you're able to replace the keycaps too and the layout here is perfectly standard which makes this easier.
For more keyboard recommendations, check out our round-up of the best gaming keyboards.