The south rd tunnels project has already risen to $9.9 billion. One would expect that the final cost will increase futher, perhaps $11B to $12B? Just a third of that could fund significant expansion and improvement to the PT network in Adelaide....
The whole thing has been over-engineered to buggery in my opinion, should have at least considered the option of an elevated road-way between Edwardstown and Daw Park where its all lined by commercial property anyway, there's no reason why it couldn't have been canvassed as an option apart from being afraid of NIMBY's - bored tunnel will take way too long and be way too expensive.
I can't see us getting out of this without a toll being applied. I think it will probably happen when Labor inevitably regain office next March since the Shoppies have been even more gung-ho for privatisation than the Liberals in this state. Privatising the whole project would at least leave them some money for other things as you say -
I'll put money on the probability that Transurban, the monopoly toll-road owner in this nation, ends up with the project as EastLink did in Victoria - probably $20 end-to-end, yet another direct cost burden for Adelaide residents to shoulder.
The Marshall govt won't spend anything to improve or expand the suburban network apart from a paltry $11m a year for the next decade for stations upgrades. Perhaps an option for those advocating for the unlikely & fanciful notion of reopening of the Hills line is to promote more pop growth in the area.
Greater Mt Barker pop is currently 38k forecast to be 50k by the end of the decade and 57k by 2036. If you get everyone in the area procreating even more than they currently are and encourage new immigrants to move there, you might increase that growth to around 80k-90k by 2050. Then a rail mass transit option does become much more possible to receive govt support and you have a decade of lobbying and canvassing vatrious options ahead of you.
Longer term the best bet is to start a social media company which becomes worth hundreds of billions and then fund your own 15km twin tunnels from Mitcham to Bridgewater with a deep underground station at Stirling.
This rampant development was never supposed to happen - we were theoretically going to have a 'no large scale development' in the hills whatsoever due to water catchment issues but for some reason Mt Barker completely ran away from them... the power of developers and their donations, hey.
Agreed, can't see inter-urban services happening in the longer term unless there's an organised group of locals who really want the service to be reinstated using the standard gauge line and the spur from Mt Barker Junction - and they'd have to battle against the hills NIMBY's who don't want to encourage more growth than is already happening. Infrastructure-wise the most formidable obstacle perhaps being sharing the track with ARTC trains and the lack of appropriate passing loops - but otherwise it's probably 'do-able' particularly if you could also use the same gauge-converted 3000's out the other side to perhaps Virginia which is in itself becoming a developer's playground thanks in part to the new Northern Expressway.
We're poor is the problem - we just don't have the rivers of stamp duty cash that NSW and VIC have or the enormous amounts of iron ore and gold that WA has. We have this 'space precinct' thing happening at the old Royal Adelaide site but frankly that's just another corporate welfare boondoggle like the Multi-Function Polis, Marshall was trumpeting the relocation of Google from Sydney to that site earlier this year but then refused to answer questions about how much money they'd given them. The whole thing is a joke, once the government money runs out those rent-seekers will be off to whoever gives them even more money...