I love my HP 24" Z24X DreamColor. It runs $549 at B&H, so I am a little over budget on this. Not as big as the aforementioned Dell U2713H, which I have at work, but I like the color accuracy and studier build of the HP.
If you are shooting video, then autofocus is not a big deal. You can get some good inexpensive lenses with precise focusing by purchasing classic Nikon primes on eBay. For $500 you should be able to get a 35mm f/2 Ai-S, a 50mm f/1.4 Ai-S and a 85mm f/2 Ai-S. You'll need a Nikon F mount to M43 adapter. If you shop wisely you can pick up all 4 pieces for less than $500 and that old Nikon glass is pretty nice.