It is not true that an ISP cannot give each customer just a single IPv6 address. The Linux box I use as a router gets a single (i.e., /128) address from Spectrum Cable on its upstream interface, and it has to explicitly ask for a separate /64 prefix to advertise on the local interface (this is called prefix delegation, PD).

So it's certainly possible for an ISP to give a customer just one IPv6 address. I'm not sure, but I think there is no rule that prefixes obtained with PD must be /64's. They could in principle give you a /126 or /127 to limit you to just a few hosts on your LAN, and charge to give you anything better. This would break stateless autoconfiguration but it would still work with DHCPv6.

Your best workaround is still www.tunnelbroker.com, HE's free IPv6 tunnel service.