the best in Bangkok is probably visathailand.com They obtain my visa. And some of visa for my friends. They are in Bangkok, great communication, great price, great skills. I send some people here too, never have any problem in this agency
I was scare about this kind of things happen to me, because im not good about administrative things, so i prefer ask an dtv agent to help me, and i have my dtv about the first time name of agency visathailand.com
I think the price depend about the case. The most important for me is not only the price, but to find agent with great communication, and able to obtain your visa, about what i see some agent have à lot of reject too. I use visathailand.com. back with my visa in the pocket yesterday.