A good option would be to source a suitable wrecked donor vehicle to scrounge as much parts off it as you need.
Obviously you need to be able to afford the up front cost for a wreck but if you work hard to fit / modify parts to fit the cobra, it can end up being a far cheaper build proposition.
A GF builder near me has used a 2004 SS ute and has made a lot of parts fit including fuel tank, wiring loom etc. Not sure with the ADR's what GM motor choice and hence model you can use, but I'm sure some one else will chime in on this.
He has sold off a lot of parts that just can't be used and has made the overall cost quite cheap. I think he is around $5k range, which is very cheap for engine/box/loom and then all the supporting paraphanalia.
Talk with Plums (Bobby) off this forum. He's a WA GF builder too who is into LS gear and can certainly help you!
Cheers and happy building.
