How much do the materials cost?
Prices will differ by area, by store, and, it seems, by the time of day. What I can tell you is that if you bought everything on the plan's materials list new at 2008 Home Depot prices, you would have paid around $570. Add in your local sales tax. Here's the approximate cost breakdown by category:
Wood, $170
Hardware, $120
Roofing, $135
Hardware cloth, $95 (The Home Depot price of this has definitely gone up since '08, so you may have to budget an additional $50 or more. BUT check too with the large farm/feed stores or wire distributors in your area. They sometimes stock bigger rolls, which may be more economical.)
Miscellaneous (caulk, wood sealer, cinder blocks, etc.), $50
I'm building an enlarged version of this coop, so my prices aren't exactly the same, but I don't think your estimate is too far off at all.
Obviously, the garden coop plan doesn't include insulation costs (but that shouldn't add much at all to the price), or electricity run out to the coop. We only used pressure treated wood on the very bottom of our coop, and chose Olympic DuraMax (I think that is the brand name) deck & fence stain to seal the rest of the wood. A $35 gallon has been enough to do two coats on all of the wood.
We also found an excellent deal on green plastic coated hardware cloth on
ebay. I got 75 feet of 48" tall hardware cloth for $60 including shipping.
We found two square (200 sq ft) of board and batten vinyl siding at a building surplus store for $58 total, and so we are going to use that on the exterior of the henhouse.
Our local ReStore (Habitat for Humanity surplus store) has windows for very good prices, so I plan to spend $40 or so for a couple of real windows for the henhouse as well.
I would keep my eyes open for deals like those, since it makes a dramatic difference in the cost.
Also, DH and I have zero construction experience (aside from being able to use power tools), and we have been able to build this ourselves. The e-book really is enough instruction to handle it on your own. I wouldn't pay someone else labor costs unless you just don't have the time to do it on your own.