I get my parts from GM in the USA. The shipping & Taxes are a fraction of the Australian prices.
The engine fits many Chevrolet, Cadillac, Buick and other GM cars so parts are plentiful and cheap (10% of Alfa prices) but they don't come in an Alfa polythene bag!
The DMF is a heavy item so shipping would still be in the hundreds of $'s - US or Australian
The seals and other bits are generally available in the UK from Vauxhall or even Peugeot/Citroen etc..
I thought about a solid flywheel conversion but went off the idea when I added up the total cost compared to leaving the DMF alone (~£1250) - after 90k there's no appreciable wear in the DMF and it works fine to couldn't bring myself to change it. I'm just putting in a new friction and pressure plate along with a new slave cylinder.
At worst I may regret it in a few hundred/thousand miles if it fails but changing it all again is not the hardest job out there.