And here's an article on a mirror of the same size as the one on MRO, .5 m, that has sufficient surface smoothness for UV observations as well as optical:

Optical Design & Engineering.
Sounding-rocket telescope uses new technology ultra-lightweight mirrors.
David Content, Scott Antonille, Douglas Rabin, and Thomas Wallace
"Two NASA-funded programs will image the Sun and then an exoplanet: both at
high angular resolution and both using the same mirror."
25 July 2006, SPIE Newsroom.
http://spie.org/x8707.xml?ArticleID=x8707

The two missions mentioned in this article had been planned to launch in 2007 but as far as I know haven't been launched yet. Since these missions are only for sounding rockets, one or more of these mirrors could be used for a Mars mission if returned safely for a soft landing by the sounding rocket.

When I first read this article, I took it to mean that the two missions were using the same kind of mirror. But by re-reading it, the passage at the end suggests it is literally the same mirror.
So this mirror could be re-used for a low cost Mars imaging mission that only carried this mirror and the instruments for imaging in the UV and optical range. You might even be able to use the same instruments used on the two missions mentioned in the article when returned by the sounding rockets.

Bob Clark