There are various services provided by agents throughout Thailand.
That ranges from "hand holding" which is basically organizing documents etc.
The client actually meets the financial requirements.
Right through to agent service where client has no funds in Thai bank etc.
The cheapest extensions without providing financials would be ~12-13k and that would be in Pattaya.
In Bangkok closer to 15k+.
Then someone using CM chimes in with 8k.
Funny.