While bellows/enlarging lens may not be as cheap as a closeup lens, the achromatic ones are not $5-$15 and the bellows/enlarging lenses are cheaper than dedicated macro lenses.....Especially if you want multiple focal lengths....
Minolta achromatic close-up lens, on eBay, can be found at that price if you wait for them. New, they are $30. at B&H. Nikon ones are also rather inexpensive on eBay and also 30$ new. Great for casual quality close-up pictures.
For high quality macro your approach is indeed one of the best for the money. Reversed 16mm normal lens is another approach. Best lenses are specialized macro optics (not common macro lenses) by Zuiko, Nikon (scientific division), Minolta, Zeiss, Leitz etc. but are also usually very expensive ($200 and over, used).
Andre
