I've often wondered about such a proposition.
A small contingent of 2 to 4 geosynchronous telecommunication satellites around Mars would allow for massive amounts of data to be related back to Earth as soon as it is gathered. Considering we have telsat birds that have been in use for 20+ years in Earth orbit, it would be easy to make some for Mars with new technology that could last for 50+ years. Such a network would be more than enough bandwidth for any mission now on the drawing board, and for those not yet imagined. I imagine it could be done for well under $1 billion.