There's no minimum to buy. The 39mm chip racks are $25 each, the 46mm racks are $30 each, USD.
Yes you can choose your wood type, the default wood type is Maple. For the racks I pictured above, they're maple for the milled parts and walnut on the sides. Those pictured don't have a poly finish yet so the walnut would get a lot darker with an oil based finish.
I'm afraid I don't offer staining on these, it's just too time consuming because of the shape. I only finish with poly or varnish.