a mechanic who said he only services VW's and Audi's said that my 2004 VW New Beetle needed a voltage regulator and that it was located under the dash on the drivers side. I

Yes the voltage regulator is mounted on the back of the alternator.

His receipt was vague and gave no detail at all. When I questioned him about the location, he said that it's "way up there and you have to work upside down to reach it. Right there I knew I was in trouble because there was no way I could contort my 67 yr old body upside down under the dash. I feel I was 'taken'. When I asked for the old part, he said that he already threw it in the trash and the trash was picked up. I'll never go back there and I out $300.