Your mechanic is trying to rape you. That's at least three times what it should cost.

To read codes, open the "A" module of the DTU box behind the right headlight, slightly inboard. Put the attached pin into port 2. Turn on ignition, do not start engine. Push the button on the box for about a second and release. The little red light will flash the trouble code associated with the problem. For example, for code 435 (O2 sensor response slow) the light will flash 4 times, pause, three times, pause, five times, then remain out. To check for a second code, push the button again for about one second. After all codes have been read, they may be deleted by holding the button down about five seconds and release. After three seconds, the light should come on. The button should be depressed for another five seconds. Make sure the codes are ereased by following the beginning procedure. If erased, you should get a 111 code. Shutoff ignition and put everything back as you found it.