Just got back from Buriram immigration office.
First:
I was told there would be a charge of 500 Baht for "Visa transfer". I told the young lady receptionist that was not right because it is a free service.
She went away only to return after a few minutes to reiterate the requirement for 500 Baht. Once again I told her that was wrong and asked why she wanted me to pay. She went away and half an hour later I was given back my old and new passports with no charge for "visa transfer".
Second:
This thing about "visa transfer" is, as others have mentioned, a bit misleading.
What I got was a rubber stamp for each original visa that was in my old passport. Information added to the rubber stamp was the date of issue, the place of issue, the type of visa and the expiry date. Also, on the next page there were a couple of stamps regarding my last extension and the date of my next extension.
I'm sure many have already said something along these lines. Apologies to you for repeating.