Bob,
This has been something I have thought about for some time also. As far as I know, there are very few matches between higher quality final output papers and less costly versions that could be used for proofing.
One that does come to mind is Epson Ultrasmooth (high end) and Moab Entrada (less costly). These seem to have fairly similar printing appearances, even though they are very different papers. For a while, I was also using some Lexjet Satin finish paper that provided a very similar output to Epson Premium Luster paper, but the blacks were not as deep and the cost of the paper was nearly the same, so not much of a deal there.
There may be more options with the matte finish papers, but I have not been using them as much, so I really cannot comment. It would be nice to have some relatively less costly paper to do proofing, and that was close enough to a final high quality printing material. One thing that I have found is using the ImagePrint RIP on my Epson 7800 printer allows me to achieve extremely similar output on a wide variety of papers. So, I can run a less expensive paper through to see how things will look (mostly to gauge sharpness, but also get some idea of how colors are looking), and knowing that the output on a fine art paper will be "close". The color gamuts and such will always be a bit different, but the profiles created for the RIP do a very good job of achieving something that is very close.
LJ