First of all, the quoted number you provided is actually for both missions, LRO and MER combined, not individually.
The material costs include:
- Time on the Deep Space Network.
- Bandwidth to serve the data to the public
- Some amount of money spent on Public Relations meetings
- Occasional team reviews, which are not all located at one location.
- Servers for processing the data
- Writing new software tools
So before I go in to the costs associated with the program, let me first explain why this is more complex than a communications satellite. Rovers have to do different things every day. Planning is required to figure out how to make it do what is desired, and what overall path the rover should take. Communication Satellites are usually relatively calm, not having significant change from day to day.
From my experience, it takes about 30 full time people to run such a system, and another 5 of them being IT support, at a bare minimum. Why so many? Several will be writing tools to make the work of the team easier, let's call that number 5. Some will be working on planning the next several days operations, let's call that number 5. Another 5 analysing the previous days operations, 5 looking at the health of the spacecraft, 5 taking some sort of leadership/administrative position, and the last 5 doing the first batch of science. These numbers might seem high, but remember that there are multiple instruments that need specific planning, plus the movements and other items. The number of people required to make this happen goes down with time, but it still requires plenty of operations. Plus there is an external scientific team, which all contribute part time to the effort, of which there is around 20 at a minimum.
So let's just say 40 full time equivalent heads, at a standard rate of around \$200K/ person (This factors administrative costs, and is actually a low estimate for skilled personnel). That would give a cost of \$10 million just for the key people, let's say another \$1 million for travel, PR, computing power, and a few million to use NASA's facilities. They also run a engineering unit on the ground, and pay some maintenance fees for the use of the various instruments (To troubleshoot anomalies that might arise). This seems to adequately fill the entire budget budget that NASA provides, \$13.2 million. This seems to match reasonably close to my estimate. Just to give you an idea, even Voyager runs \$5.3 million per year, and they have a team of only 10 people.
I suspect that LRO is similarly priced. While you don't have to drive LRO, you do have to plan for a lot of images, and that requires substantial work. Each instrument will be planning their possible images up to 3 weeks in advance, coordinating with each other team to ensure they can point the spacecraft in the right direction. The team size and cost are thus similar for the two.
Bottom line is, these two spacecraft do an enormous amount of work, for a small amount of money. But I don't think one could reasonably reduce the cost of the missions.