"Normal hours" 1500 baht, or 30 USD (I think, on the USD as I have never used to cross). Extra charge of 200 bhat if you forget to take a photo...
Pretty simple, go to a window (the right hand one is best as that is for return of passports & so never a queue) & ask for the forms. You will receive two... one is the visa application, which you must fill in, hand into the left hand window along with passport, photo & money!! Guy will check & then tell you to wait for its return from the right hand window!! If you like you can now fill in the other form which is the arrivals/departure card. By the time you have nearly completed that your passport will appear (by a hand waving it in the air - no verbal confirmation, so you have to keep an eye on that window all the time - especially as they do not come out in the same order they go in) you will have a full page visa stamp in your passport & need to add the number of it to your 'arrivals/departure' card.
The actual passport processing is pretty dam quick, mine was about 10 minutes max - queuing up to hand over the form & passport is the time consumer.
Now you have your visa & passport back proceed on round to get immigration to give you an entrance stamp - more (usually long) queuing.
When you have your stamp proceed on to pay what I think is a 'customs' fee - 50 baht for Falang, 20 baht for Thai. You will receive a ticket as proof of payment, put it in your passport because in another couple of steps you will meet a policeman at a barrier & he will want to look at it all - this only takes a couple of seconds though. Now you are in Laos & in the middle of all the Tuk Tuk & taxi drivers!!!!!
If you are not going into Laos then you can ignore them all & wander towards duty free. Do some duty free & then cross back over & get an exit stamp & clearance. This is not as time consuming as waiting to get in but there are usually a bit of queuing.
WARNING it is VERY easy to completely by pass this exit process which won't cause you any problems until you try to get back into Laos the next time!!!
I also know that some people have done the visa bit then by passed the actual entry & exit stamp. There is a notice (in English) at the visa processing stalls that says if you do this now & get caught you will be fined 100 USD.....