Lol at $400 for injector cleaning. The other stuff is ridiculous as well. Sounds like the workshop was trying to take advantage of you.
I do agree, I DIY most things on my car. But judging by the OP's post, he doesn't have much experience with these cars/engines. In my opinion, he should get it serviced properly and well checkout out the first time. There's a lot that could need changing that he might look over if just changing the oil, ie. belts, brake pads, rotors, etc. etc.
Then once he has had the car for awhile and has got some more experience with it, DIY to his hearts content