To earn $100 per hour +GST, would cost 5k+ for a VF stainless cat back, TIG welded with custom fabricated mufflers and not many will pay that for a Commodore exhaust. Euro car enthusiasts will pay it when top end bolt on's are 10k+ and a full custom system is much cheaper.
I've done plenty of full custom exhausts over the years when crunching the numbers, earned $15.00 per hour and didn't make apprentice wages.
I've seen a dual full stainless header back exhaust with high flow cats, 2 resonators and a couple of mufflers in the rear, all tig welded with nice bends, all tucked in tight and knocked over in under 2 days, I think the guy paid around $2k total for the pipe and labour, he did supply the cats, resonators and mufflers though, if I recall correctly he used Racecraft gear, the shop was Liverpool Exhaust
His car, VF Clubsport sedan, sounded epic, loudish, but not heat seaker loud cruising around, and zero drone
After a quick look at the Racecraft site just then, the parts that he supplied cost him around $1.5k, so a total cost of around $3.5k for excellence
For a cat back subtract the cost of the cats and that bit of labour, so under $3k
My custom stainless header back, with cats, to 3" Y pipe, to 4" single with a custom made resonator to fit under the VX (that space under the rear passenger seat) and a big off the shelf muffler in the rear that took less than a day to make, sounded epic, and didn't drone, costing only $1500 drive in drive out, again at Liverpool Exhaust
Disclaimer 1: I did get a noise warning once by a friendly member of the constabulary, so later fitted a 4" Varex muffler in the rear for keeping the constabulary happy when pulled over for "random" breath tests, and when driving into, and out of, the neighbourhood during early morning leaves or late at night arrivals, when closed the exhaust is as quite as stock, when open and cruising it's loudish, but "nice" and no drone at Hwy speeds, even with a slush box (which is amazing), but when open, and I'm up it hard it sounds like war
My advice to the OP is to shop around and buy to your budget, in the end it can be alot of coin if your putting it on a standard engine for some noise, unless of course you are planning for alot more mods and power down the track
Or, if you still run the stock headers and cats on a stock engine just replace the rear boxes for the sound you want, a cat back on a stock engine/headers/cats won't give any noticeable power gains, just noise, but.....only a couple of hundred for each nice straight through mufflers of your choice for the rear, that fits well and let's the noise out, plus labour to install them, is money well spent IMO for just sound on a otherwise standard car
Disclaimer 2. I'm grumpy and over opinionated, just ask any of my family or friends