Answering my own question, per Tripadvisor reports Grab are not allowed into SAI

Found another bus operator with slightly more frequencies - https://www.facebook.com/photo/?fbid...04525563284028

Can prebook taxis at getyourguide or booking.com for $35/40,
It also seems there is a transport desk at the airport where you can organize taxi for a similar (set?) rate. Not sure the hours, seems to be 8am-8pm
Per TA, taxis are currently fleecing walk-up fares, asking $60+ oneway into town