There are a TON of beautiful coops on this site that have been made with less than $500. It can be done, but you'll have to earn it.
I am always amazed at how much "trash" lumber one can procure from a construction site. The waste is remarkable. All you have to do is ask. I even had guys load my car for me - talk about service!
I had multiple friends come out of the woodwork when I was building my coop with house windows and misc. building materials - one even gave me some free metal roofing for the run since his insurance company was replacing his pole barn roof after a hail storm. Free - just come and get it. Saved lots of money as good windows are pretty pricey.
The final step is always to paint. Do the trim. Pay attention to the small details. Paint or stain all wood the same color. So much mis-matched materials can be unified with paint. And it protects the wood. I stained all the exterior wood with waterproof deck stain - including the run posts. Much easier to do it before the hardware wire is attached.
Best luck!