How much should I sell my old PC for?

[ZoltecGames]

About a 5 year old pre-built machine, built by Dell. (Dell XPS 8500) Had no problems with it for the duration of use (used it all 5 years)

Specs include
i7-3770 CPU (stock intel cooler)
2TB HDD (5400 rpm)
GTX 660 1gb
16gb RAM (ddr3 I suspect though I can find out if it matters a great deal)
350w PSU (not sure on this one but it was able to run a GTX 960 SSC when I had it in there)

Mobo has surround sound capeablities
x4 USB 3.0 Ports (2 back 2 front)
x6 USB 2.0 Ports (4 back 2 front)

As a side question I assume upgrading the GPU on this old rig would probably be the most beneficial thing to do, what card would you recommend?

 

[Dark Lord of Tech]

$225.00-$250.00

 

[ZoltecGames]

$225.00-$250.00

is that CAD or USD?

 

[Dark Lord of Tech]

US

 

[ZoltecGames]

Cool and oh almost forgot, it came with a 24" 1920x1080 6ms responce time ISP display with HDMI that is of course also 5 years old what should I ask for that?

 

[Dark Lord of Tech]

$50.00