Little help with pricing p226 9/.40

A buddy of mine is getting rid of his p226 9mm. He wants to sell it to me with an additional .40 slide. The gun has had two owners and it was originally sold in 2002. It is in good condition, not amazing. I'm going to fire it this weekend to see how I feel about it. What would be a reasonable price? Ive been told 550-900 but that's a big gap, and I don't think it's worth 900.