We don't scan any more - we just found we weren't actually doing enough with the information to make the cost worthwhile. I just checked our accounts - one scanner charged £40 for 15 ewes (I think that was their minimum charge) and another charged £70.
It would be worthwhile doing in your first year as it's useful to know if one is born, whether to look for a twin etc, but after that, it depends on your own system, and particularly whether you'll get rid of any 'empties' before lambing time or not.