How to get to Hong Kong Disneyland from Regal Riverside Hotel in Sha tin? Hm does it cost?

Well, there is no direct transportation between these two places. So you need to transfer.
From the hotel, take public bus no.E42 at Greenfield Court to Lantau Link Toll Plaza. Then transfer to Bus R8 to Disneyland directly.
It costs 19.9 HKD per adult. And the travel time is around 65 mins.