domestic flight ticket at travel agency?

I want to fly from Sapporo to Okinawa in the middle of March. I have no experience with buying domestic tickets in Japan. Is it possible for me to go somewhere like JTB or a different travel agency here in Kobe and just buy a ticket there? Will I get charged much more this way as opposed to doing it myself online or something? If not I'd like to do so, as it sounds easier and my ability to read kanji isn't the best.

Thanks.

Buying air tickets online won't cost a fortune these days. Skymark often offers very reasonably priced tickets.

http://www.skymark.co.jp/en/index.html
https://www.ana.co.jp/eng/index.html

There is no direct service between Sapporo Chitose and Okinawa. Therefore you need to buy tickets from Sapporo to Tokyo and Tokyo to Okinawa separately, and need to transit at Tokyo Haneda. Allow plenty of connection time.