If cost is a factor - which I’m guessing it must be for you to be basing yourself in Kannai (may be a false economy staying there, but I don’t have enough data to push this) - then the cheapest rail option would usually be to get to Yokohama on a different train that takes about 30 minutes longer than the Narita Express.
However - there is no significant cost saving to be made as you will have a foreign passport and, so long as you are returning to NRT within two weeks, you will be eligible for a discounted Narita Express return ticket
https://www.jreast.co.jp/e/pass/nex_round.html
From Yokohama Station you can get to Kannai Station, takes 5 minutes and 140yen.
Make a print out using Google Maps to get from there to your hotel. Or hail a cab at Yokohama as suggested.