you don't need to buy a re-entry permit, if you have got a multiple entry tourist visa (METV) when you cross the border back into Thailand by most land borders, you just need to fill in the TM6 arrival card, and present that along with your passport and a printed pdf copy of your METV to the immigration officer, and make sure you check they have stamped you in for 60 days, before you walk away.
I would say it's a ticket to the Thai/savannakhet border, not savannakhet itself, but anyway it's a matter of opinion I suppose, but the opinion that matters, is the opinion of the people issuing visas, and I read these visa pages quite often, and people seem to always suggest they will only accept a flight ticket, showing your exit plan within the time you're stamp in for, and a bus or train ticket will be rejected, personally I've only ever purchased a cheap flight ticket to a neighbouring country, and it's always been accepted.
yes I've been on that bus from mukdahan to savannakhet, but what Brandon thurkettle is trying to tell you, the bus stops at the Thai immigration, you stamp out of Thailand, it then it goes across the friendship bridge and stops at Lao immigration, you then need to buy a Lao visa, and walk around on to the Lao side, and arrange another bus or taxi, to go into savannakhet, the bus you crossed the bridge on, it then turns around and goes back to the Thai immigration, and then back to mukdahan bus station, I've done it few times doing border bounces.
the Thai visa process is only easy for people that have educated themselves, it's only simple when you're experienced, I'm still learning everyday. ð ð
I have been in Thailand now for 7+ months on an METV, I did the border bounces at the thai/Lao border myself, with no problems whatsoever, you basically just stamp out of Thailand, cross the friendship bridge on a bus, fill out a simple Lao visa form, you can pay for the Lao visa with Thai baht, its āļŋ1700, you just need a passport size photo, and a printed pdf of your METV, and obviously your passport, you can leave Thailand at the Lao border and come back the same day if you wish, when you return back to Thailand you just need to fill out the TM6 arrival card. If you don't want to do it yourself, depending on your location, there are border bounce companies that take you to the border and back again, if that would be easier for you.
Are you aware you can get 8 to 9 months out of the METV visa?? Check the expiry date on the visa, it should be valid for 6 months, if you do a border bounce just before it expires, and after that a final 30 day extension, that gives you 8 to 9 months in total.
Go to the immigration office you will be doing the extension at, and get a list of requirements, for instance some will require a TM30, some won't, Just do the extension when you have 7 days or less left on your current stamp, because some immigration offices won't allow you to do it earlier than that, the 30 days will be added onto your current stamp end date.