There is a very nice 'onsen' in Narita town, excellent if you have a layover or if you have extra time after you've landed and before a business meeting. Nothing better than an invigorating shower followed by a relaxing hot soak after a long plane ride. The standard, traditional bath (all I've used) is only $10 or so, though they also have full spa services. Like most onsen, they also have a cafe serving food.
http://www.yamatonoyu.com/eng/
It's in Narita but perhaps getting a cab from Narita station would be easiest. It's not the gaudy 'water park' near the station; Yamata no Yu is further away - print off the map from their website and hand it to the driver.
