It always is!

The marketers of those pre-fabs are taking advantage of folks like you who have no experience and don't know differently... yet.
Lots of folks talk about free ranging to make up for the lack of space their coop/run provides but the problem with that comes when the birds start jumping fence lines and taking off. They will. Or when the little darlings start digging up your flower beds and pooping all over the steps, deck, porch, car... fill in the blank. You get the picture. Or when you get your first predator attack and need to confine the birds for a week or two. Then behavioral issues start because the birds are cramped and bored.
Visit the coop pages for lots of ideas on building a coop from scratch using anything from standard lumber to free pallets or converting a shed or part of a shed into your coop and building a run onto it.
Good luck!