On a 202 C-class, new pads and disc should cost about $150 - excluding labor and some low dollar misc. parts. If the brake fluid wasn't flushed, and a pressure bleeder wasn't used, I would say weak brake line or master cylinder or damaged ABS unit.
If brake fluid was flushed, air in system.

Is the pedal pressing close to the floor? or does the pedal feel a little softer? I find when you do the C-class front brakes sloppy - no brake cleaner to clean channels and reusing old bolts with incorrect torque the pedal does seem to feel a little less firm. But this is a less than exact or proven observance.

Does the pedal build up pressure when you pump it? both engine on and off

Pedal will not firm up or rise over time