Did this last week no problems at all. I'm lazy so used the Cambodian touts that hang around just over the border to fill in the paperwork Cambodian visa tm6 etc and tipped him 200bt. If you want to do it all yourself it will be no problem. They will just walk away no hassles.
The current costs are 1500 for visa and 300 for quick turn around. However the Cambodian IO on entry insisted on 1800 and would not budge so for the sake of 300bt I just paid up and then had to pay the guy doing the exit stamp another 300. Still cheaper than staying a night so it was worth it.