There are some plastic 6x 4 shed on ebay from argos at the moment for £200 apiece - easy to add a pop hole branch and perch + ventilation holes. (and a shelf for food storage?)You could also build a roofed walk in run big enough to add on for another £100 if you got the avery panels off ebay.
So for £300 you'd end up with a solution that would actually give your hens much more space, be nicelywinter proof and easy to clean out for far less than the cheapest omlet offering. It would also give you the option of expanding your flock to 6 or so if you catch more hens disease.
Can you tell I'm considering this option for our new house as one Go is not going to be enough. 
. DS & I have a bad dose of more hens and our chicks are just 3 weeks old! (2 pullets and 2 boys - we'll hang onto to one lad the other will go in the oven).
To be fair DS has been involved with community farms since toddlerhood, we've just never had our own garden before. So I know it's not just a phase (as he actually enjoys mucking out!) and at nearly 10 is old enough to take proper responsibility for looking after them with adult oversight. I am sticking with bantams so he can help with tasks like wing clipping and checking for mites as these are small enough for him to handle with just my supervision rather than the properly qualified bods at the community farm.
cuckoo marans bantams seemed to fulfil my requirements of being fairly hardy & clean legged in a wet climate, reasonably good egg producers, autosexing & not too flighty. (some of the bantam breeds are very prone to mareks, don't produce enough eggs of a reasonable size, have feather legs which can cause problems in mud etc, etc).
I think we'll keep the Go + 2m run long term just as a sick bay/broody space and adapt a plastic shed + walk in run as our "main" coop for our adult birds. If I had the money I'd spring for a greenfrogsdesigns coop instead of the shed or a cube, as these have really impressed me when I've seen them in the flesh.
I'm not 100% convinced about getting ex-battery hens if you are a first time chicken keeper as they need quite a bit of tlc & healthcare knowledge at the start. It's easier to get healthy hybrids while you learn about chicken keeping. They also don't seem to live more than a year or two after rescue, going on the experiences of friends, which can be very upsetting for children.