flight from Siem Reap to Phnom Penh

I need to book a flight from Siem Reap to Phnom Penh. does anyone know any reputable travel agents? and how much should this airfare cost?

If you have a credit card, you can book e-tickets online here:
Siem Reap Airways

$74us one way inc all taxes/charges.

World Express Travel. Half a block from the south corner of the Old Market (Psah Chas) kind of across the street from the Ivy Bar as you're walking towards the Red Piano.