When I last bought silk tubs for my fixie they were around £100 each. The premium-brand tyres for my Land Rover were also £100 each last time I bought them. The main difference is that the silk tubs generally lasted somewhere between 1,000 and 2,000 miles, and I usually get 100,000 miles from my Land Rover tyres.
If I compare tyre cost and wear rates with my more typical bikes and cars, then bike tyres still end up costing more per mile.