I picked up a pair of Solognac Inverness 300 hunting trousers from Decathlon for 45 quid and they got a first run out on Sunday morning.
They are double-thickness heavy-duty cotton with a waterproof membrane sandwiched in between and feel really durable (they have a 2 year guarantee which seems generous at this price point!). Billed as wind-proof, water-proof and thorn-proof.
Sunday was cold and they kept me dry and warm (but not too warm!) while walking and also for periods spent sitting or prone on the frozen (at first) and then muddy (later) ground. No rain to contend with but most 'waterproof' fabrics can repel falling rain, whereas prolonged pressure contact with wet ground is probably a more valid test. We weren't yomping miles up any hills so can't really say for sure how breathable they are but the fact the inside surface is cotton, rather than an exposed membrane meant you didn't get that clamminess next to the skin.
I presume there are other folk in my position where lack of stalking opportunities and/or funds (...OK, the wife!) make it difficult to justify spending £££ on the top-end gear so you might want to have a look at these. For me, they seem a good upgrade from the previous pair of Craghoppers ...