Talk to me about follow focus

[AKturnanburn]

I'm trying to setup a rig with my 5D3 and a 150-600mm for video. are there many options under $400 that work?

[SUPERIOR]

I have worked with both manual and wireless follow focus systems.
I find that follow focus systems work well when pulling focus on a commercial shoot with a large(r) monitor.
Are you planning to bring a field monitor to your ski shoot?
If not, you should think about shooting with an increased depth of field and a very basic follow focus.
Don't laugh, but maybe think about a product called Lens Straps http://www.lensstraps.com/
Otherwise, you're spending lots of money for a very small increase in quality.
That said, if you're super serious about investing in gear, go with a Red Rock Micro system or one of its Chinese clones easily found on Ebay.
Tons of follow focus advice available on Caleb Pike's DSLR Video Shooter website too, FYI.