I would look into gathering used materials if cost is a problem. Pallets, old barn wood, cinder block, bricks, etc. also, if you use a site like Craigslist you could post wanted ads and watch for any useful materials.
Best of luck.
I copied the information below.
From http://m.humanesociety.org/animals/foxes/tips/solving_problems_with_foxes.html
"There are several scare devices that are both humane and effective at keeping these extremely sensitive animals out of areas where they are not wanted.
Noise-making devices...