If you want just a QR plate, then I suggest that you get one with a common form factor for other mounts. You don't mention whether you already have a ball head, but if you do then look at QR plates for that brand.

I recommend the "Manfrotto 323 RC2 Rapid Connect Adapter with 200PL-14 Quick Release Plate" for $33 on Amazon. The Manfrotto mount is very sturdy, releases quickly, but has a safety lock to avoid accidental release. This will work if the diameter of your monopod mount plate is about 2" or less, otherwise you would need to use an adapter. This is a robust mount, and the QR plate is compatible with the Manfrotto 234RC pivot head as well as many Manfrotto ball heads if you decide to add to your equipment.

Or, you can look at an Arca Swiss clamp. This is a standardized mechanism that a lot of companies support, compatible with L-plates, ball heads, gimbal heads, etc. I recommend the "Desmond DAC-01 50mm QR Clamp 3/8-inch w 1/4-inch Adapter Arca Compatible for Tripod Head" for $25 and the "Desmond P-50 50mm QR Lens / Camera Body Plate Arca Compatible and D-Ring P50 DP-50" for $10

As you can see, the recommended solutions all run about $35, but provide a more robust and flexible solution. You can go the cheaper route, but there are two things to think about:
1. You have an expensive camera, and you don't want to drop it because it's mounted on a cheap clamp.
2. You can invest in a system that provides expansion and consistency.