You have a hostel near the big intersection of the Thai embassy Hide @ Seek
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0 kip per night. Then you have a few hotels in the area. The cheapest is Laongdao1, where you can get rooms for
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0 per night at the counter. The quiet rooms are those behind the hotel. You have more expensive hotels of course. The best one is Grant. Enjoy Vientiane and don't try to limit your stay to rush back to Thailand.