Luggage storage at the airport is available at the airport:
http://www.narita-airport.jp/en/guid...svc_06.html#t2

If you're capable of carrying your suitcase and you're on a tight budget, I'd suggest hauling it to your hotel; you'll save a couple of thousand yen over the course of your visit. The trip doesn't need to be terribly arduous. There are escalators to the platforms at Narita and at the stations where you arrive in Tokyo. If you stay near one of those stations, you might find it manageable.

For a hotel that's in your price range and quite convenient to the airport, I'll make my usual plug for Hotel Lungwood in Nippori. Yay, Lungwood!

You can take the Keisei line to Nippori station. The Keisei Skyliner costs 1,980 yen, but there are also somewhat slower limited express trains that take a little longer (71 minutes to Nippori) and cost 1,000 yen.