Yes, if you have tools (or in my case, a handy husband with tools). Cost depends on size, design, and the materials you select.
That said, if you're not under a time constraint where you need it immediately, keep an eye on CL and your local FB groups. Since racks are expensive to ship you can find some screaming deals locally on used enclosures and rack systems.
There is a lot more instructions. The hardest part about building a snake rack is to making the exact measurements and cuts. If they are off, you will need to make adjustments which can be a little annoying. It is easier to buy, but cheaper to make.