It's near impossible putting definitive values on these RR lenses. I bought an unnamed 20" RR lens about 2 years ago for £120 approx 135 euros the seller was asking £300. it's in near mint condition it'll cover 15"x12".
I agree with Ron somewhere around £100 to £140 would be average for an RR lens taking Waterhouse stops, particularly as there's no flange or lens hood, and maybe not a full set of Waterhouse stops. Many RR lenses have a screw in lens hod, or sometimes it's part of the front cell casing, some lenses though didn't come with one, the Optimus did have a screw fit short lens hood and in 1898 your lens a 14" 10x8 and 105/- (shillings) £5 5s (£5.25), in comparison a similar f8 Dallmeyer 13" 10x8 RR was £8 10s (£8.50) Your lens was also available with an iris diaphragm for 120/- £6
Someone who has a Perken 10x8 camera though may well pay more to have a lens to match the camera.
Ian