what should a new oem computer for a 1996 cabriolet cost?

Hard to say, depends if new OEM computers are even available, or if he is quoting you a factory remanufactured unit. Best option is to call a VW dealer with your VIN number. They will give price and availability as mechanic is likely adding some for having to find the part for you. Most ECM units that old are remanufactured. The $400 labor sounds high as well. A dealership should be able to replace and re-flash the ECM in about 2-3 hours in most cases, which would come in well less than him even at $85/hour labor, which is high in the PA area.

Thank you LH, I went into the VW dealer (associted with Ford for some reason?) and they only offered a refurbished model at $1500.00; They did not know if a new one was available, isn't that odd? The VW dealer thought the $1700 plus $400 was a good deal. I just don't know.... I'm going to think about it and get a second opinion. I've taken lots of cars to this guy, mostly small stuff, tune ups, etc, but once for an overhaul of my CRV for $2200.00 he isn't fast that's for sure, his service is in a Mobil Station. Thank you for your response-- I am car clueless! R

Are you sure it's not O2 sensors or catalytic converter?