The absolute best A/C shop in California, IMHO, is in D&S Auto Air in
Costa Mesa California, probably I bit far from the central coast.  I'd
give GoWesty a call and ask them for a recommendation closer to home.
However just in case you really do want the best:

D & S Auto Air
1661 Superior Ave
Costa Mesa, CA 92627
(949) 645-7802

Interestingly I found a link with their address and a map:
http://www.imcool.com/shops/dsautoair.htm

They've done work on lots a Vanagons, including Subaru conversions, and
my TiiCo conversion.  Steve is an amazingly honest an upfront guy with
uncommon integrity for a "mechanic".  I'm sure he'd gladly give you an
idea over the phone of what was involved in a R-134a conversion.  I know
it is a lot of work to do properly, personally I would and personally am
staying R-12.

-Jon

Sharon Mendonca wrote:
> Can anybody suggest a reliable A/C shop for conversion to R134a in California?  We got a quote from a local a/c shop for $900, who probably has never worked on a van (whom we didn't trust) and then we went to another local VW shop.  Quote was $420 to begin with and ended up at $1,600 - we decided we didn't want A/C THAT bad.  We would still like to convert sometime, but not for that price.  We're located on the central CA coast, but can travel wherever.  Any good suggestions?
>
>   Bob & Sharon Mendonca
>   88 Westy
>   88 Vanagon GL
>
>