Like anything it is 100% dependent on what you want... I scavenged wood and siding from some construction sites (with permission) and built ours for the cost of the nails... Of course, it doesn't match from one side to the other and its a little Frankensteinesque... but it keeps 40 chickens happy and laying and warm in the winter. You don't need to worry about insulation too much (ours did fine in -17 degree weather last month) but it does need to keep drafts out...
I'd guess you could buy materials and build a nice one for under $500, even if you weren't trying to be thrifty... then again that's twice what I paid for my last car, so I'm not the best comparison
there are quite a few good chicken coop plans out there on the internet, but like I said - it all depends on how handy you are, how much of the construction and design you can do yourself, and how much you care about how it looks. Chicken coops are pretty simple little structures. I paid a total of $20 for hinges and nails.
