Looking for info on a samyang f5.6-7.1 100-500 mm zoom lens for a canon camera and the price for a used one?

This lens is sold under the Phoenix label in the US, Samyang is the Korean makers label. Not on anybody's recommended list. You can find it under either label on eBay for under $100. Don't pay too much, you're net getting much and it may not work with your EOS camera in AF mode. You can always use it in manual.