...Well, I wouldn't exactly call it cheaper. Those two lenses together cost more than my 100mm macro lens. Just the 70-200 alone costs more than the macro lens, lol.
It probably is one of the cheapest ways to go past 1:1 though.
And heck - if you already have 2 or more lenses, why not? Ideally, you would want a long one and a short one. Long lens divided by short lens equals magnification. 200mm/50mm = 4:1
You don't want to go too extreme though - 4:1 is hard enough!
Working with this setup is pretty tricky...
I still don't have any focusing rails, so I have to focus by moving the subject up and down. DOF at f/32 is probably about a half a millimeter or so. The total focusing range possible (by turning the focusing ring) covers like maybe 1 or 2 mm, so you have to position the subject pretty damn close to where it needs to be.
I'd rather have the MP-E 65, lol! But, till then...