Do you need to have a licensed contractor build it for insurance or regulation compliance?
Because if you don't, you can get much more affordable work from a handyman type (but verify their reputation, and pay in allotments as work is completed).
Our very first coop was built by a friend's roommate with some carpentry skills, he did a really good job for less than $200, and $400 for materials (back then). Of course, that was a special circumstance, but the point is there are options.
Try to really look around at what's available near you. Ask some people you trust like at your church or work or friends if they might know someone handy that can follow the plans you give them.
And, adding an apron is not a big deal. If every little detail is nickel and dimed, then you're being taken for a ride.
We see this guy at the swaps near us, he shows up with a trailer laden with his "builds". They are uncovered pens made of chicken wire and mismatched scrap wood, from pallet wood to dog eared fence boards. He asks $200 each and I've heard him give his spiel to people, "never lost a bird in one of these".
The crazy thing is, he obviously gets enough customers to pay for the business logos on his vehicles, website, etc. People get taken advantage of more than usual in niche markets like chickens (and horses, gardening, etc.). Just be extra careful.
