Copy and use the code you will get 15% discount for each airport transfer booking on GoAsiaDayTrip website. These booking can be applied in all the nations in Southeast Asia.
The cars are private and high standard will help you to have the most comfortable trips.
I still think it is not expensive for someone who want to use private car with high quality service. Moreover the taxi drivers can cheat you by driving the long way to get more money.
Don't just go and pick any taxi from the airport. There are plenty taxi services like yours that you can book in advance; just google "Private taxi transfer Bangkok to Pattaya", and you will get plenty of reputable companies.
Just checked with one of the taxi service in Thailand (BKK to Pattaya): it's 37 USD while this service quoted 70 USD or 59.5 USD with discount. I think I will book with the taxi service.