I have a Multi Entry Non Immigrant O visa and just used the Chiang Saen crossing to get another 90 days. First I was told by Thai Immigration that I had to spend the night in Laos but then he saw my visa. With the visa I didn’t have to spend time in Laos, just got stamped in, stamped out and back to Thailand for another 90 days. As I was leaving I saw some guy without a visa and he told me they were going to require him to spend the night there so he didn’t go.
Boat to Laos is 70 baht each way. The boats need to have 3 or 4 people before they leave and it might take a while now as fewer people are doing their runs here, and if you’re waiting for a boat and another boat drops off passengers but you’re the only one waiting for a boat they will leave empty. Lao visa is $40 US or 2000 baht, and they want crisp bills and they will reject old looking USD. Lastly, Thai immigration is really good up there.