How much should I expect to pay for a yew bush about 50cm tall ?
...and, where would be the best place to buy such a thing ?


If you are not in a hurry you could always grow them from seed for free.
I've got around 20 plants grown from seed gathered from the yew trees at
Chatsworth House while on a visit there. They are not particularly fast
growing though, so you would be waiting a few years for them to get to 50cm.

Drakanthus.