if u enter/leave Thailand to go to Laos ur not converting anything:
your getting a new Non O visa
so just enter with visa exempt, You MIGHT be asked for forward or return ticket
Onward charges only $14
NO::: has to be in ur name
so deal with that before u leave thailand and arrive in Laos, only need show its been there 1 day
note afaik, it can be 400,000 or equivalent in any currency