Hi Max,
Yes, I'd say it's Strathearn. They made these in at least three sizes. The basic weight was formed and then pressed into a mould for the "star" shaping. £20 is a reasonable price for your example.
I assume the "fit for a doorknob" comment was intended as a rather derisory remark. I don't think the moulded "star" pattern was actually used for Doorknobs, but certainly standard domed weights were. They were made by Strathearn, and earlier at Vasart, and Perthshire Paperweights had their versions too - and those are particularly well made. I have even seen a photo of a Doorknob with the paperweight part made by Paul Ysart, but I have not seen one by him for real. The Doorknobs are widely collected, and many folk still use them for the intended purpose - I once visited somebody in Scotland who had Strathearn Doorknobs on most of the doors.