Sadly they aren't worth that much anymore because they are a few years old. I just looked on ebay and there isn't one on there above $500 and has similar specs to yours minus the APR. So I would guess for your system probably $500-600
That is what I saw on e-bay also. I was browseing the Dell web site since I get a company discount and a coworker saw me and he said he would give me $500 for my 8600 if I was wanting to sell it. I'm not really wanting to sell, but was curious about the price.