Why did NASA decide on one big rover instead of 2 smaller ones?

The Mars Science Lab is $1.2 billion and climbing while the MER's were about $400M each and provided coverage in two locations. Why did NASA choose to do one big rover instead of two smaller ones (that probably could have stayed on schedule) ?|||They already have the two there, like you said? They probably want to save money, I mean they COULD build two smaller, less sophisticaed ones, but this one will be like a... SUPER ROVER... heh, and I don't really think they need many rovers on mars, at least for now.|||I think it's because they needed to have one that could rove further and be independent of solar power (it will have an RTG). They probably just couldn't afford two of them.|||in addition to the above points - it's also cheaper to have one than two because it does not take multiple launches and space craft to get them there. One big rover also allows you to specialize the mission or have a rover that's more multifunctional|||Probably a better question is why they launched two MERs in 2003, rather than one. They did because they could. They had built two rovers and had two rockets capable of launching them. Because they'd had such bad luck with Mars exploration, they decided to go with redundancy. You can read all about it in Steve Squyres' book, Roving Mars.