Hit "Customized Appraisal" then punch in the options that the max has. It will take an excessive mileage hit of $1100 (so deduct that from the $3500)
I personally wouldn't pay more than $2500. Also, the one thing I would absolutely, positively check is the last time the previous owner had the timing belt changed. Nissan required a 60,000 mile timing belt change for that engine...and the price can range from $350 to $650 to do that work. If that timing belt is old and breaks while your son is driving it (particularly highway speeds), then you'll spend >$1000 to get the engine rebuilt. So that's a definate must!
If the car needs a timing belt soon, then I would deduct that from the price too. Goodluck!
PS: Better yet, you may want to have a mechanic look it over before you buy (check the transmission, brakes, engine, etc, etc, etc)...if you're buying from a stranger.