put a 2920xm in that baby. i just picked one up for my m18x r2 and it works like a charm for less that $100 usd!
then you'll need to see what heatsinks you have if youre going for a bigger GPU (like the X80m series) its going to be putting out ALOT more heat, same for CPU if you overclock, i recommend atleast the dual heatpipe for the CPU.
SSD, a basic 120GB for OS.
at least 8GB of ram, 16GB recommended,
all in all, if you need to upgrade all the heatsinks for heavier GPus and a CPU. that is going to be around $100, ssd (for a 120gb) about $40, Cpu $100, plus whatever you get for GPUs. so expect to drop around $500 for a decent upgrade probably way more. for gpus. but dont forget to take into consideration what you can sell your old stuff for when budgeting it out.