Make a Market FS thread following the guidelines.
Set a price as high as you would like, then link back to your thread here and ask for price suggestions (or wait for the Price Police )
if your PC is around 3 year old, you can start with 60% of the price you paid, except for the GPUs bought during mining boom.
if the price is high, people will surely negotiate or you may reduce the price if you're not getting enough response