Space.com has an article on France pushing to constrain the ExoMars rover mission targetted for launch in 2016 to a smaller budget. This is a continuation of a long going debate within ESA and its funding countries on the ambitions of this mission.
Some editorial comments:
NASA and ESA are talking about combining their efforts for a 2016 rover mission. However, one ESA official was quoted as saying that ESA would want to develop its own technologies for this mission. While I understand national pride, I don't think this makes best use of scarce funds. NASA has a tremendous investment in precision entry, desent, and landing. With the MER rovers, it was difficult to find interesting places that had large landing footprints and were suitable for airbags (the ExoMars planned landing system).
The United States has tough laws on technology export (and I personally think too tough). If Russia launches the mission, it may be difficult for NASA to contribute much.
ExoMars started as a roughly 800M euro mission, perhaps a bit less (as I recall). If you simply want to go somewhere with interesting geology, you could do a good rover mission for that amount, I suspect. I have a geologist friend who focuses on Mars and he would love to put a MER rover in a couple of interesting places to groundtruth the orbital data. (MER cost $650M several years ago, as I recall; in inflated dollars, $800M would probably be reasonable swag in today's dollars for a mission to launch in 4-6 years.) However, the focus of rover missions for both ESA and NASA has moved to exploring locations that may have been habitats for life. That requires sophisticated instruments and rovers that support them beyond what the MER rovers could do. ESA and NASA have both costed rover missions to do this type of work in the ~$1.5B/1.2B euro range. (NASA and ESA include different items in their budgets so direct comparisons are not simple.)
Because of the success of past missions, Mars is becoming an expensive place to explore. The missions that address the cutting edge questions seem to start at ~$1B (Mars Science Orbiter or network mission), go to ~$1.5B for a solar powered rover, and then jump to $3-5B for a sample return mission.