Really depends what you mean by "worth the time". There's the Polish girl in St Ann's who'll famously blow you for £20, she also does FS at £30 for 15 mins.
Also check out my last review, a couple of nice gals who were each £30 for 15 mins, and were really good fun. I think they might have upped their price a tenner since though.
But all of the above are big lasses, which is fine by me, but not much use to you if it's not your bag.