Motherboard manufacturer and model is almost always silk-screened onto the face of the board. It is usually near the first PCIe socket. or CPU/Northbridge chipset.
If it is an AM3+ AMD board with 8+2 phase power, I'd say an FX 8320 or the FX 8350 on sale will be a hair under $190. If it is a current Intel board, I'd say a non-K i5 4000 series will also run near or a little below $190 on sale.
* Always check manufacturer supported CPU and RAM lists for your specific motherboard before buying.