Hey Easton Coop, i am an Englishman here in America, welcome to the relaxing world of chicken keeping. Coop looks excellent, i am trying to persuade my Dad to convert my little sisters old playhouse into a coop, nothing better than fresh eggs.
I think a mate of mine paid something like 5 or 6 pounds (sorry no stirling symbol on my keyboard!) per chick. If you have an auction near you you can get them cheaper and already laying, i promise you though, after a couple months with them you will want to raise some chicks, so go easy on the initial purchase and spread out the additions over time! I pay about 2 pounds per chick here.
I know a lot of the same breeds are available, i assume you are allowed roosters, i have never heard of an area not allowing them at home, so you could always raise them from eggs and cut the cost there. If you want eggs and good layers, try a rhode island red or plymouth barred rock. The Sussex are beautiful chickens, rarer over here but my mate has loads of them.
Good luck, just make sure Fantastic Mr Fox doesnt come and pay you a visit!
Matt (currently in California, from Northamptonshire originally)