Cost of new sliding patio doors?

[Shufflebumnessie]

We're planning on decorating the lounge in the summer but before we begin we need new sliding patio doors.
I'll be getting quotes from a few local companies but I'm curious if anyone knows roughly how much it will cost to have new doors installed. I dont want to be too shocked when the quotes start coming in!

I paid £900 a couple of years ago , that was to turn a window into a sliding door. They chopped out the bricks and made good on the outside but not the inside.

We are in South East London and paid 9500 for 4 sets of 8ft x 7ft aluminium sliders this summer

Thanks for the replies. I'm hoping it'll be closer to chicken's cost.....

That was the cheapest we could find... upvc were much cheaper but have heard horror stories of expansion and contraction and our doors are all South facing