Cores, Duo, 2 processors in one scenario. Quad, 4. (some are just 2 cores in hyperthreading). Instead of one core running 100 processes, it is 2 cores, or each core running 50.
Don't make the mistake that others do. If a quad core runs at 2Ghz, it is NOT 8Ghz. You don't add the cores.
in the price range of motherboards, it depends on the chipset and features. USB3, Wireless, # of SATA ports, size of board (ATX, MATX), number of PCI/PCI-E/PCI x1 ports, the grade of integrated sound, if it has video onboard, the gfx model, etc. Plus the manufacturer. Some cheaper boards are lower grade in features than the big boys.