Quotes for ACO around house

Firefarie71

Hello. We recently purchased a home and the previous occupier had a patio installed. Its too high and we need to have a ACO installed to the back, side and front of our home. Ive received three quotes. One for £550, one for £1000, one for £1200  and an online estimate of £2.5 to £3k. Ive asked the tradesmen if they provide a warranty/guarantee and one said they dont. One does (the £1k quote) and still waiting on a reply from the others. 

This is new territory for me. Any advice would be very welcome. 

I have attached some pictures, which might help. The 'drain' at the back in the pic is filled with concrete.

Thanks in advance for your help.