What is the value of my computer?

I need to sell my imac because of the credit card interest :( Unfortunately I messed up and didn’t pay it off in time and the interest killed me. No matter what I’m losing big time here but I just want to get rid of the debt and be done with it.

I was wondering what is the fair value or what can I ask for when selling it. I spent 1200 on and I know Ill be lucky to get at least 700 now.

2.4 GHz intel core 2 duo processor
3GB 800 MHz DDR2 SDRAM
Snow Leopard 10.6
No damages of course. The mouse scroll ball probably needs replacement if anything.
500GB hard drive

I don’t know whatever specs matter…oh it’s the 21” screen I think is the size.

What would be the best way to recoup the debt for this computer/how much can I sell it for?