seeking cheap, good afghan
Don't know the places you're referring to, or the exact price range you have in mind; but there is a very good Afghan restaurant called The Helmand in North Beach. I wouldn't call it cheap, but it's not unreasonable; two can get a very nice meal for $40 without hooch (obviously more with).
re: Tom Hilton
Yes, Helmand's a great place, reasonably priced for it's style and quality. And Mr. Karzai, who runs it, is a great guy, charming and personable.
For a similar, but downscale experience on the Pakistani side of the border, try Shalimar on Jones Street in San Francisco. Lamb chops to die for!