As with anything check the prices elsewhere. Clutch hydraulics are a classic. The pre-filled master cylinder with hose can be upwards from £175. I think the current S4P price is beyond that. I got a Borg & Beck cylinder only for £55 and plugged in the reservoir and pipe. Ditto the slave. Any more than £40 is silly and they often don't really need replacing. Mine looked really rough so I replaced it but when opened up the inside was as good as new. It went on Mrs Dave's car because her bleed nipple was rusted up.
On the other hand, a pair of front shocks were about £10 more than Fleabay but proper Magnetti Marelli parts are with the seal bit extra. Ditto the clutch. A nice Valeo for 100HP was actually less than what was on offer on eBay and they stocked the oil seal I needed.