We've purchased basic beaded foam blocks (30" x 30" x 40") for our bowhunter ed classes and have had them last for years (in class and in our yard). We'd dump it in the bed of the truck for classes, then put it back in the yard for our own use. We'd replace the foam block about every 5 years - that's a lot of broadhead and field point use.
More recently, we bought sheets of ethafoam, glue 2 sheets of foam 3" deep X 25" X 25" together and made our own self healing targets. Add a wooden frame to help keep them vertical and you're ready to shoot.
The most durable home made target is sand. Probably the best sand target I've seen was a cube frame wrapped with foam and filled with sand. The 2x2 wood frame kept everything square, the foam kept the sand from leaking out too much, and you never have to worry about shooting all the way through 16" of sand.