Not sure if Aalco is nationwide, but we are building on a budget and cheap as possible is the best option.
Metal prices go up and down so who knows how much it would be next week.
I personally would look about and price the cheapest/best quality I could find.
The reason for mentioning Metal supermarket was this,an 8x4 sheet would be a fortune possibly £100 or more at their prices.
Update,Aalco have 17 service centers around the uk from Aberdeen to Plymouth.