Well, I've also been looking at this question and I have been to quite a few reclamation yards, as well as looking on line. What thickness are you looking for, and what material?
My experience is that real limestone flags are hugely expensive - £80-£100 per sq metre - so for 40sq m you'll be looking at (gulp) £3,000 - £4,000! I'm not sure about other materials like York Stone but I'd be surprised if they are much different. The alternatives are concrete (cheap and nasty but practical for the back yard), reconstituted stone (not quite so cheap or nasty, but a bit twee perhaps - too ordered for an old house IMO) and imported stone (which costs a lot less than reclaimed limestone - a lot comes from India I understand).
Beware of anything which is too thin - in my view the limit is 20mm, but on the other hand reclaimed limestone flags tend to be of variable thickness which makes for challenging laying! I will probably settle on some 40mm thick imported limestone in a suitable colour and in a range of sizes. The stuff they describe as "tumbled" seems to have a good soft appearance and I can get this at "only" £32.50 + VAT per sq m. This will come from an Oxfordshire yard where I also got my black limestone flags for my kitchen floor (see my blog from 2011 http://houseintheenchantedforest.blogspot.co.uk/2011/06/limecrete-floor-part-3-laying.html). It's a job for when it warms up but I'll order it soon.
£3-4k on a patio does sound excessive. But on the other hand, I don't want something that looks a cheap immitation. Do you think the Indian Limestone aged/tumbled flags look convincing enough?
You could try Castle Reclamation at Martock, Somerset - they have a website. They do concrete-fake flagstones. That sounds horrendous but I know several people who have them and they look fine. They come in different stone types like blue lias. I have no idea how they compare on price but the people I know who have them aren't rich.
Yep, I was going to suggest them Vicky. They took casts from original Charlton Mackrell Blue Lias flags and they are very good. These flags were always laid with no grout in the joints in fact they were laid with the edges touching each other. This was achieved by chipping off the undersides until they were straight.
Castle Reclaimation also have lots of genuinely reclaimed flagstones, including some rare hamstone ones ( I'm hoping to grab those this week to relay some of our hall that someone replaced with concrete) although not on their website. In fact most of the reclaimed ones are hidden away in their '2nd' yard down a lane about half a mile from the main public yard at Parret Works. If you ask in the office they'll take you their but you won't find them on display.
I fell in love with their ' pretend' but very realistic cobbles, until I was told about the difficulties of laying them and the cost. But a great stockist of flags
Interested to hear about Charlton flags, are they similar to the Keinton ones?
The Forge, I know the second yard well. Spent many a happy hour there while doing our place looking for just the right sort of bricks. They are very helpful people. Their great blocks of ham stone are incredible - a stonehenge in orange hamstone in the making, eh