I think you are mis-reading their chart. I just checked again and it clearly lists BKK to Pattaya 1200 for sedan...1500 for SUV...and 1800 for van.
I used them again just last month and as always, excellent service, vehicle in good condition, and driver was wide awake and drove sensibly.
If you prefer the bus, nothing wrong with that. But as a frequent visitor to Thaialnd, I am skeptical that bus is any safer then taxi sedan. Thai news reports feature rather spectacular bus crashes almost daily. And you still have the minivan drive to deal with.
But as they say...up to you.