This is the cheapest XPS 8500 desktop on Dell's site.
If you're curious about upgrading to a Core i7 processor, it's actually a decent value. At time of writing, the price difference between this base config's Core i5-3350P and Core i7-3770 was about $110 if you just bought the CPUs from Amazon. Dell is charging $125 for that upgrade, so it's at least in the same ballpark, and you'll have it straight out of the box instead of having to swap the part on your own and then hope to resell your leftover Core i5-3350P, for which it would be hard to get full retail price from an individual buyer.
However, DO NOT add on a monitor that Dell offers you. When you click to the customization page, Dell labels the 23-inch S2340L monitor as "Dell recommended" for $189.99. What a joke. We found they sell it separately for cheaper than that.