I have a $99 external screen that works well but is not stellar. A few questions:
Do you need to:
- record the camera's LCD screen settings
- or only display what you're recording
Do you need the external screen to:
- pass the video signal through to your computer
- or are you only recording to the camera SD card
Do you need:
- a 4K screen
- or just Full HD (1920x1080)
Update: I originally assumed you want smaller (5"-10") camera- or tripod-mounted monitors. But if you have a computer in the mix, you could use two (19" or larger?) monitors. With a laptop, you'd need a dual-HDMI docking station; a desktop might have dual HDMI outputs already.
Camera > HDMI > USB Converter > Computer > (Docking Station) > Dual Monitors
If no computer, you could see if daisy-chaining two monitors would work:
Camera > HDMI > Monitor 1 HDMI In > HDMI Out > Monitor 2