I am assuming you are capable of building a coop since you included that as one of the options you considered. If so I am curious why you chose the more expensive option, and indicate you can add on or modify a kit. You could modify or add on to a coop built from scratch and it will be built a lot better. I am in the process of building my coop this weekend, the research I did I could not find anyone who recommended the "kit" coops. I purchased all the materials to build a 6x8 foot coop with 7 foot walls and an 8 foot peak roof for right at $300.00 from Lowes. The only material I didn't purchase is the metal for the roof, I am repurposing that. I bought treated lumber for the floor and floor joist which was a big part of the expense and also bought smartside for the walls. The rest is a bunch of 2x4x8's that are under $2.00 each.
I would bet even if you had to pay someone labor to build it for you, you could get more bang for the buck buying materials.