Space Computer
The computers that power Spirit and Opportunity are BAE Systems RAD6000’s. They run at 25 Mhz (not a typo), and cost $300,000 (also not a typo). Here’s two articles about them.
I guess what you pay for is the radiation hardening, the greater temperature range, and the higher mean time between failures? The RAD6000’s MTBF is rated at over 375,000 hours. I can find some server-grade PC motherboards rated at about 30,000 hours. I don’t even want to know what consumer stuff is rated at.