cheapest way Narita to Shinjuku

we are a group of 8 seniors, hope to find cheap and easier way from Narita to Shinjuku washington hotel, is the shuttle bus 1500yen each way?
do we need to buy in advance from overseas or if we hv to purchase at airport? where and help?
and from shinjuku, whats the cheapest way to go to Yokohama cruise terminal, any bus from shinjuku?
is free wifi easily found in shinjuku or tokyo too?

we are a group of 8 seniors, hope to find cheap and easier way from Narita to Shinjuku washington hotel, is the shuttle bus 1500yen each way?

The cheapest would be an uncomfortable bus/train ride via Tokyo Station (1200 yen).

The next cheapest would be an uncomfortable train journey with a transfer a long the way (1230 yen) using Keisei limited express via the Keisei Main Line and the Yamanote Line.

Almost as cheap would be access by Narita Express with the NEX Tokyo Direct Ticket (1500 yen). It is very comfortable, except for the 10 minute walk from Shinjuku Station to the hotel.

The most comfortable would be the direct bus to the hotel, but the cost is a 3100 yen.

do we need to buy in advance from overseas or if we hv to purchase at airport?

No advance purchase is required. Unless you are interested to buy the Japan Rail Pass, which only makes sense if you do some long-distance train travel during your stay in Japan.

and from shinjuku, whats the cheapest way to go to Yokohama cruise terminal, any bus from shinjuku?

Take the Marunouchi Subway Line from Shinjuku for just station to Shinjuku-Sanchome Station and transfer to the Fukutoshin Line. Some trains along that line go all the way to Nihonodori Station, which is a 5-10 minute walk from the pier. The one way fare is 650 yen.

is free wifi easily found in shinjuku or tokyo too?

It is becoming increasingly easy, but can still be challenging. You can improve your changes to find it with some advance research:
http://www.japan-guide.com/e/e2279.html