I was wondering how the MER package would integrate with a Falcon 9 rocket for eventual future Mars exploration on the (relatively) cheap?

My idea is that they'd dust off the old blueprints of the MER's at JPL, build a couple of them, integrate them (transit stage, EDL package and all) on top of a Dragon 9 and then fire it off towards Mars. Would be a proven exploration package with no extra research needed, sent off on a (hopefully) cheap and reliable rocket.

Does the MER heatshield fit inside the proposed Falcon 9 fairing? Could it carry one of maybe even two MER's?

Do you think we could get Musk and JPL interested in the idea?

We've just scratched the surface of Mars with Spirit and Oppy. Seems to me you could get a lot of valuable science by sending a small fleet of identical MER-type rovers to various Martian sites.

Steve Squyres said in an interview that he could not see the benefit in flying the Athena instrument package again.

He also wrote that he would have preferred not to have squeezed MER into Pathfinder base petals because there was a high risk that the rover might not completely unfold, which would end the mission prematurely. Presumably this means that NASA would be reluctant to launch more unfolding MER style rovers again.

A disappointment I have with MSL is that there is only one of them. However, I do understand that the cost of a second MSL might have been more than $500 million dollars.

MSL's landing site selection process identified a number of very different sets of rock types at the different candidate landing sites. I am hoping that more than the 2 planned rovers might visit Mars over the next 10 years to visit these diverse landing sites. I think that the diversity of landing sites would justify flying the same mission twice.

the big problem of the MERs and of the airbag landing system is that they could land successfully only in a few flat, relatively uninteresting areas.
for what it's worth, one of the Mars Polar Concepts of the latest decadal survey, is a MER-class rover to land within the polar layered terrain using precision landing techniques (probably some kind of Skycrane)

They would have to fit within MAVEN's and ExoMars Trace Gas Orbiter's availability ―Mars Odyssey, Mars Express and MRO will be running out of propellant after 2015.

Or maybe SpaceX should run their own relay orbiter and rent it, since TGO gets so little love.