As far as a mount goes, get this one http://www.amazon.co.uk/gp/product/B00HZ0JJGE
. It's sturdy and in your price range.
As far as an active display adapter, this is an example of one, the StarTech Active Adapter http://www.amazon.co.uk/gp/product/B004SUELLC
. Make sure you get one that is compatible with your outputs on your graphic card. This one is likely to work.