i did post that if i was doing it i would drive there myself, and also avoid the 'agents' fee, but without your own vehicle and having to hire a car or car and driver, the costs are starting to rise, car hire, fuel and Cambodian visa would come to 3,000 ish baht plus any back handers that are required, so i think that the link that ubonjoe posted and at 4,000 would not, at this present time for an effortless trip, be too over the top, this is the price that people have to pay to either stay long term in Thailand by repeated visa exempt entries, or to change visa class to something better for them.
i in the past used ban pakard/ pong nam ron for reentry stamps for a multi entry non imm 'O' visa, i think then the cost for DIY were under 2,000thb, and a mini bus from Pattaya under 3000thb but i could be wrong