Information published elsewhere, but I thought it worthwhile to give this a space of its own as the other stuff’s spread across a couple of posts.
Crossing is easy – that’s the first thing. Don’t sweat it. We went from Bangkok to Siem Reap with an overnight stop, but if you can be bothered with an early start it’s easily achievable in a single day.
Stage one is to get to the border. A train is the cheapest and easiest way – you want the service from Bangkok’s Hualamphong station to Aranyaprathet which at the time of writing was 48 Baht. A superb resource for train journeys all over the place is The Man In Seat 61.
There are two services a day – 5.55am and 13:05pm. Taking the first, you can get to Siem Reap no problem. With the second I’d recommend an overnight in Aranyaprathet rather than over the border in Poipet, though the latter would be cheaper from what I hear. Maybe. I gather it’s not so safe, though.
Either way, you’ll have a 4 1/2 hour train ride with some great scenery (and no air conditioning). On arrival at Aranyaprathet you will of course be greeted by tuk-tuks prepared to take you to the border or to a (“cheap”) hotel.
Also either way you will end up at the border at some point. If you already have a visa then head straight for the crossing. Otherwise you’ll have to go to a separate office elsewhere (tuk-tuks know where) at which point you will be fleeced for the visa fee.
Right now, a Cambodian visa is $20. You will pay this in Hanoi, Bangkok, Saigon, Auckland, London… $20. Yup, it might take 2-3 days, but that is the visa fee. You’ll also pay $20 if you land at either airport in Cambodia and pay the fee on entry. $20 and they put the big paper stamp in your passport.
However, get it at a land border… at Aranyaprathet they ask for 1000 Thai Baht. At the current rate of exchange, this is $33. You can “save” $3 by saying you don’t have any Baht, and they’ll let you pay in US currency at a fee of $30. The “excuse” is that the $10 is an express fee, though they don’t offer a means of paying $20 and waiting 2 days. It also doesn’t explain the immediate visa at the airports without such a fee. The presence of overseeing government officials at the airport, however, does.
Short version – $30 at land borders so the staff can line their pockets.
A short tuk-tuk ride away is the border crossing itself. You disembark and a Thai will likely assist you through. There’s no real need for this, but they’re not pushy and slightly helpful. Of course, they expect a tip afterwards for this non-requested and non-essential service. Stamp out of Thailand and into Cambodia (after filling in one of those annoying immigration slips), then walk out into Cambodia proper.
There you will be herded onto a tourist bus which will drive you over the incredibly potholed road to an office where you will be sold a taxi or bus. Taxi is $60 to Siem Reap (around 2 1/2 hours with the new roads), bus is $10 and around 4 hours. The roads are much better than you’ll have heard about historically and work is still being done on them. The little bit up to the tourist office is by far the worst you’ll experience.
Now you can get a cheaper taxi, but it’s difficult. You’ll be actively discouraged (harassed) if you try to barter outside the monopoly system. The driver gets $25, the monopoly some money and the government (apparently) some more of the $60 fee. So theoretically, you should be able to find a private driver for $25. Good luck. I did meet some guys in Siem Reap who’d got one for $45 by refusing to board the tourist bus – just say you’re going to check the casinos or something.
Good luck, however you do it. It’s not a difficult crossing, and the experience isn’t bad. Quite an adventure, really!