So many good questions, so many bad answers
Zubrin's price tag is 20 billion. NASA's was 50 billion for Mars Semi-Direct, but has gone up I think. In either case we are looking at expenditures over 10 or more years. At 2 to 5 billion per year this is a sizable fraction, but not even half of the manned spaceflight budget if it is around the 10 billion I think it is. No impact on robotic missions is needed.
see ya