There's another thing to consider, that hasnt been mentioned yet (unless I missed it). If $40k is your budget, make sure you're leaving yourself a couple grand as a buffer, these are great cars but certain things can and will fail, as on most ten year old cars. When I purchased my '97, I had the car sent to John Vasos for PPI before I even laid eyes on it. He basically told me i'd be a fool not to buy it, and that it needed nothing. Needless to say, i've spent many thousands to make the car perfect, some expenses necessary, some not (same when i purchased my '91). You may not have a desire to make/keep the car in showroom cond as I do, but you can virtually assume the clutch hydraulics will fail, a cam plug will leak, at least one O2 sensor will go bad, at least one coolant hose will fail, hatch and/or trunk struts will go, the driver seat bolster may need minor repair, and you'll have to keep an eye on the wheel bearings/axle nut, catalysts, battery terminals, Bose amps, and climate control unit, and budget for more frequent tire replacement.
Clutch replacement on the 6spd is muy expensive b/c of the dual-mass flywheel. The earlier models would add window regulators, ABS, and oil press gauge to the list, as well as the snap ring issue on the affected cars. NSX's are also rock chip prone (most don't consider a pleather bra a viable option), if that bothers you then you'll have to budget for clearbra or repaint of front bumper cover and side vents every few yrs (varies of course). Very few dealers are competent with these cars, so you may need to budget to have the car sent to a capable tech for the major svcs, i.e. T-belt/water pump/valve adjustment. Lastly, I would recommend oil chg, transaxle fluid, brake flush, ABS flush (yes they're 2 separate systems), fuel filter, air filter, PCV, spark plugs, and spool valve filters if not done recently, plus I would test all the coil packs and inspect the coil cover gaskets. You can do a coolant flush and change the t-stat and cap as well.
Oh, and try to find one of the ones that's under emissions warranty extension, mine is and it is absolutely FANTASTIC. Expect to pay more if the seller has one of them and knows what it is, but I assure you it will be worth it.
Hope that helps man.