My 2nd coop was awesome and all made out of recycled material. The house was framed with treated 2X6's that were used as a road for a drilling company.....the job was over and the locals could help themselves. Imagine a 1/2 mile road all made of 2X6's..... the siding was from a trailer that needed to be ripped apart. The fence was cypress branches, put into the ground with used tin nailed to hold in the birds. Above, in the trees, was a very strong rope, with a trawl hanging, that canopied the whole coop and yard. I felt like I was in my little piece of Heaven when I was in there. I laughed so much at the chickens antics, especially when they'd be playing football with DH's cigarettes.
I now have a much bigger coop, which costed a lot, but the fence was not expensive. I use 2X4 wire 5' high and metal fence posts, I get at Lowes. I guess you can just see what your budget allows. $100 can give you a small run. Guess it depends on what type of chickens you have, such as will they fly (but you can always clip the left wing feathers). Also depends on if you have a preditor problem. I've used clothes line wire to form a canopy to drape deer netting, so the hawks can't get my birds. I paid $13 at Lowes. If you can do that, then you can probably go with 4foot fence posts and wire to save money. We used zip ties to hold it to the wire and to make splices in the netting. Come to think of it, that was also pretty, but not as pretty as the trawl canopy.