Getting the DTV extension in Bangkok was easy. Here's my experience and how I think about the idea of going on a border bounce.
Going to Immigration Office: I had my documents prepared. They open 8:30am but I was there 7am and I got queue #233 but I was #1 to visit Counter J where they extend DTV visa, so the wait was short. The interview and review process was pretty quick, they looked over every document and cross referenced financials, and they asked a few questions, then gave me a preliminary stamp. I do have to make a second trip to the I.O. to officially get my stamp in two weeks, but the officer told me if they accept my documents in person (which they did), it's 100% sure I'll get my extension.
I prefer this method to the border bounce.
Here's why.
While the time spent queueing at an airport for the first flight or standing in line at the IO is roughly equivalent, I believe getting my new stamp will be very quick compared to the second flight's queueing. Plus, printing some documents was much easier for me than having to go through the logistics of planning a two-way flight, hotels, and taxis.
In terms of costs: It only cost 1,900 THB for extension, under 500 THB for transportation there and back using Grab car, and I did my document copies at a shop near my home for cheap so it cost only a couple hundred baht for those. Not a big financial hit at all when it comes to well under 3,000 THB for everything and I'm home the same day.
Oh and I also did my 90-day report and Residency Certificate in the same day so it shows how quickly things can get done at the Immigration Office.