TheAnalyst,
OK, I'm from Sydney so these may not be national but might help your thinking nonetheless:
Electrical: We used
Lawrence and Hanson. They're a wholesaler but you can walk in as an owner builder and buy at wholesale prices.
Timber: Don't go to Bunnings. Find your local timber supplier. We used
Warringah Timbers and they're about half the price of bunnings for lumber.
Plumbing: Again find a dedicated plumbing supplier. I think we just used
Hardware and General because most of my plumbing supplies were sourced by my plumber so I didn't need much. I also used hardware and general for my door furniture as I went during a sale and got a good price for the lot.
Fitout: Try a local auction house. We used
Laws for the most part. My wife sourced our bathroom vanity which is a really gucci one with integrated rectangular raised basin for $400 from auction. These retail for about $1500. She also sourced the toilet, skirting boards, architraves, tiles, all the paint and all of our blackbutt tongue and groove flooring from auction. The blackbutt cost us $7K and we laid it ourselves. To get someone like SE Timber to do it was quoted at $25K odd so we saved a packet. Similar story with the paint which we sourced at half price then painted the entire house inside and out ourselves and saved $10-20K odd. There must be an auction mob somewhere in Perth.
Kitchen Goods: We used
Winning Appliances. They're a discount whitegood type supplier. We got our 900mm stainless steel oven with integrated cooktop plus stainless steel rangehood for about $2,500. I can't remember the brand but it wasn't Smeg or one of the top of the range ones but it was still excellent quality with cast iron trivets and a central cast iron grill plate etc. I think its a DeLonghi from memory...
Hope that helps a bit.
Cheers,
Michael.