I'd argue, having just looked at Shark Designs, they are just a tad exorbitant M'Lud!!!
For example: the DMT - Diamond Mini-Sharp (Fine)(F70F) is selling for £18.95, whereas an ironmongers in Brighton (Aird & Co), who I'd normally class as expensive, sell the self-same item for £7.95 which has the plastic guard too.
As it happened, they were also selling (again, the same item) but in a pack of three (fine, rough, extra fine, for £7.95 without the plastic housing … so I bought those!
So think on young skywalker.