You can use T-111 plywood. Comes in two thicknesses. You put it right over the studs. It has vertical grooves in it.
Ron

Is that a treated wood? Is it paintable?

I checked out the T-111 at Lowes $26 a sheet...any other suggestions?

You can use regular exterior ply and just paint it. Use solid 1x3's at the corners, eaves, seams and door to protect the ply edges and give it some architectural interest.
I don't know of a lower price point.
Ron

You may also buy exterior plywood and using a router bit make your own T-11 siding.
Do you have access to wood pallets?
Strip the pallets and use them as siding.I build my shed using old pallets.A labor intensive job but when you get the pallets for free why compolain. I used a solid stain on mine.
You could also paint them.
Let us know what you end up doing.