Repco sell the oil pressure switch socket for $18 I think it is. I had the same problem and fixed it myself by replacing the oil pressure switch.
Oil Pressure Switch - $65 (from Holden)
Oil Pressure Switch Socket - $18 (Repco)
The problem was annoying me for a few months... was so glad to finally get it fixed for only $83. Actually I sold the socket to a friend a couple days later for $10, so the repair only really cost me $73.
As for the price of the oil pressure switch I think I got very lucky. Rang local Holden dealer and this is how the conversation went;
-ME: Hi, I'm after a price for an oil pressure switch for a VZ
-HOLDEN: They cost $279 but we are out of stock
-ME: Wow, really? $279? That seems like a lot!
-HOLDEN: Ok hold on I'll double check the price
(put's me on hold)
-HOLDEN: Ok they're actually $169 but we still don't have any in stock
-ME: That still seems like too much, I was just on the phone with Ultratune and they quoted $120 to replace the switch, including parts and labour, but there is a 2 week wait on the switches
-HOLDEN: That sounds too cheap, they must not be using genuine parts
-ME: Nope, they are definitely using genuine parts... He told me they were waiting on the switches from Holden and is unaware of any aftermarket replacements
-HOLDEN: Ok let me double check again
(puts me on hold again)
-HOLDEN: Well we do actually have them in stock and they are only $65. Sorry for the confusion but that part has been superseded a few times and I had to track it back through the system. I also don't normally work in this department, I'm just filling in for the day
-ME: Excellent, see you in 15 minutes
I haven't heard of anyone else getting the switch for any lower than $65... best alternative I found was about $85 off the net somewhere, can't remember the site.