Cost: about 1500 yen
Duration: about 3 hours
1. Take any "ordinary" Keisei express train (not the "Skyliner") bound for Ueno, and get off at Nippori or Ueno (70-75 minutes). The fare is about 1000 yen.
2. From Nippori or Ueno, take the Yamanote Line train to Shinjuku. This is a JR service, so you have to transfer from the Keisei station to the JR station in each case. It is much easier to do this at Nippori, because the Keisei and JR stations are adjacent. When you get off the Keisei train at Nippori, go up the steps (following the signs for JR). Before you can pass through the ticket barrier which separates Keisei from JR, you will need a JR ticket to Shinjuku. This costs about 190 yen, and is available from the ticket window. Just show your Keisei ticket, and say "Shinjuku". You will receive a JR ticket in exchange for your Keisei ticket (and cash), and you show this at the barrier. The Yamanote Line is a "circle line", connecting the main central areas of Tokyo. It doesn't matter which direction you take, but the "anticlockwise" direction is shorter (and this will be indicated by a sign on the platform saying Shinjuku in English). It takes about 20 minutes to reach Shinjuku.
3. Follow the instructions in "the fast and easy way" for the trip from Shinjuku to Minami-Ohsawa.
Cost: about 1500 yen
Duration: 2-3 hours
1. Take any "ordinary" Keisei express train (not the "Skyliner") of Keisei Main Line bound for Ueno, and get off at Keisei Yawata (about 40 minutes). The fare is about 800 yen.
2. Follow signs (or ask directions to) Motoyawata, on the Shinjuku Line subway (5 minutes walk). Take the train to Hashimoto (about 700 yen). Express trains run every 20 minutes until mid-afternoon on weekdays, taking around 70 minutes to Minami-Ohsawa. At most other times non-express trains take around 90 minutes to Minami-Ohsawa. If no trains for Hashimoto are indicated, take any train and transfer to the Keio Line at Shinjuku (as in "the fast and easy way" for the trip from Shinjuku to Minami-Ohsawa). (It is also possible to transfer to the Keio Line at Sasazuka.)
The Shinjuku Line begins at Motoyawata, and this is the great advantage of this route: you will certainly get a seat for the entire trip to Minami-Ohsawa, and you can keep your luggage out of the way of the crowds. When buying a ticket at Motoyawata, the easiest method is to pay about 200 yen and then pay the rest at Minami-Ohsawa. (It is possible to buy a through ticket, but you have to press a button on the machine which puts it in Keio mode).