It all depends where it is made. The very best fly lines, especially floaters, are American and to the basic cost must me added import duty and shipping costs.
The best lines have far more critical quality assurance than the cheaper lines. The cheaper lines are sometimes called "mill ends". You can get some very good mill ends, you can also get some horrible ones.
There are some very good lines now manufactured in Britain, especially sinking and intermediates. Airflo make the best sinking lines in the world in my opinion. Their "Glass" clear intermediates, are lines every fly fisherman should own.
Airflo floaters however, are not up to the quality of the best American ones. This is a personal opinion of course.
I have just purchased a new line today as a matter of fact. It is a Wickhams weight 6 WF floater from Yorkshire Game Angling at ?29.99. I've just spooled it. It feels great, very slick and supple. I'll let you know how it fishes in future posts.
Quality lines can "felt" immediately you cast with them.