Siem Reap to Pai, Thailand

The bet way would be to fly to Chiang Mai with Thai or Bangkok airways then get a minivan from the Arcade bus station up to Pai. I don't think Kan airways fly to Pai from Chiang Mai now. Or do you mean cheapest route?

Cheap is always good, and flying is fine, just wondered if can go overland easily. Probably not, I'm guessing, without a motorcycle (and a driver!)
thanks for your thoughts. What happened to Kan Air?

Can go overland just takes time.

bus to border then from Aranyaphatet either get bus to Bangkok and bus or train up north or go via Sakaeo, Saraburi to Lop Buri and pick up train to Chiang mai

take a joint cab ride from SR to osmach border north of SR, take a Van to Surin, take the Chiang Mai bus. This itinerary avoids the crowds at Poi Pet.

Vans from border to Surin, very often, good road, low price.

Chiang Mai bus - price based on the class you like (VIP, 1st etc.)

cheapest version:
bus to Poi pet border, train to BKK, train CM
2 trains a day from Aran to BKK. Your butt will feel the pain

#2 I'm not sure whats happened but when I search for flights on their website it is only displaying a return option not any flights to Pai from Chiang Mai.