I've made a 4X5 using a 130mm f7.7 lens from a trashed Kodak 1A folder given to me. The lens has front cell focusing to 6 ft. so all I had to do was space it at infinity from the film. Made from hobby plywood and foam core total material cost was less than $15 not including 4x5 film holders. So I'd say it was a cheap 4X5. The cheapest I could make at any rate and depended on a free item, the broken Kodak 1A.
Regarding a light lens for 4X5 (it wouldn't work for this book camera) the aforementioned lens from the Kodak is only 110g/3.8oz.