A shout out for https://www.reglaze-glasses-direct.com/ for their excellent service. Send them an old lens, or tell them the diameter required, along with the precription you need and a new up to date lens will cost only around £12 posted. I've heard of figures of £30+ quoted by RFDs and "specialist" opticians.

The parameters you need to give are:- Pistol, distance sphere prescription +0.75 and Rifle, distance sphere prescription +0.5. Also give cylinder and axis as stated by your optician.

Thanks to Robin C for the addition values.