I have a 1999 A4 1.8T (pre-split), and the side mirror glass needs to be replaced. ECS Tuning has the driver's side replacement for ~$60, but all the passenger side mirrors are ridiculously expensive ($120+). Are there any other websites that sell these?

 

Go to a salvage yard and get the glass off another car. Pre-factory A4 obviously works but mirror glass from a B5 Passat or a C5 A6 also can be used as a donor - they're both direct fits. I used one of each in my car.

 

On ebay over here in the UK, can get them between £3.50 AND £10 GBP

If any help to you

 

cheapest place you can find is the best place! OEM is gonna be the best quality hands down like Jeremy says junk yard