Very rare. The positive side is we now know how they are made, although I suspect there may be several different types.
For those who have Selman's first auction catalog from 1990, take a look at lot 53 "Painted weight with portrait of an elegant lady", 4 1/2" diameter; $1,600 to 2,000 estimate, sold for $2,320 including the 10% bidders premium.
The auction listing points to other references including the Encyclopedia of Glass Paperweights by Hollister (page 183) and the Art of the Paperweight by Selman (page 92). The weight in the Art of the Paperweight is the same as the one in the 1990 auction.