Other questions to consider: Is the coop designed for your climate? If not, is the coop -easily- adaptable as built--i.e. can you add ventilation, insulation, etc., without too much redesign? And, do you have the time and skills to build a quality coop? And arre you willing to use recycled or cut-price materials to cut costs?
We are currently in the middle of building a coop that is likely to cost us $1200+. That is for 6' x 5' coop + 6' x 7' run, a gravel foundation to deal with extreme freeze/thaw cycles for our MN climate, a strategy following the best advice for size, ventilation, cleaning, etc., traditional building methods including framing, insulation, sheathing, vapor barrier, siding + roofing--and I'm sure I'm forgetting something!
Anyway, to make a long story short: if I had known how much time and energy this project would have cost my husband and me, I would gladly have picked up the telephone and asked a few questions. We are not saving any money by doing it ourselves!