I think the best value would be to go to your local butchers. You can keep prime cuts like fillet, sirloin, racks of lamb to a minimum and have more of the cheaper cuts for stews and slow cooking. Great for this time of year!
And use vegetables, lentils, pulses or meat-free alternatives to pad out dishes and make the meat go further. Buying joints like whole chickens rather than packs of chicken breasts will always be cheaper and you will get several meals from the joint.