I did an upgrade a couple years ago for MWO, first upgrading my obsolete and refurbished MSI Twin Frozr GTX 260 up to a refurbished MSI Twin Frozr GTX 760. Both were factory-overclocked, and both cost me less than $200, and I haven't had any issues with them. The upgraded graphics card helped a lot, but I found that my largest improvement came from the CPU upgrade. I went from an AMD Phenom II 965 Black Edition that was overclocked to 3.7 GHz to an Intel i5 6600k at 3.5 GHz stock. With this combination, I'm running MWO at a combination of high and very high settings and I get between 60 and 90 FPS.
With that being said, it might be worthwhile to pursue a CPU upgrade first. You may need a new motherboard for compatibility reasons, but with the newest boards, you will be able to make upgrades to your machine for awhile.
I highly encourage you to learn how to build a computer. It isn't really hard as long as you understand where compatibility between components matters. YouTube helped me a lot when I built my first machine. It kind of goes together like a Lego set :)