Yeah like Andrew said, Security Camera TFT monitor testers but there's one 3.5" screen model that mounts to your wrist, and they can come in and around your budget. I'm keen to try one out, but they seem to be popular with FPV quadcopter enthusiasts, so resolution seems pretty good. If you're filming it, you might need to have some output cable adaptors but they're certainly the most compact and cheapest option.