Can I use IPv6 today?

The answer is no. And yes. You CAN use IPV6 internally. You CAN provide your wewbsite with IPV6.

If you provide your website with IIPv6 ONLY, all people on IPV4 will not be able to access our website. Which means 99% of your potential visitors are off.

It is that simple.

Nice to prepare. Bad to use at the moment. At least exclusively.

provider offers unique IPv6 addresses much cheaper than IPv4

If that is not for free, run. You should not get addresses, but a full network, and upon requst I think a /56 or something. That is what the specs say.

If your server is on IPv6 and your workstations are on IPv4, they will not talk to each other unless you put in an IPv4-to-IPv6 bridge in between. Good thing is there are a number of different services that provide just that. HE is a common one. So is SixXS.

Of course, you need to make sure that the VPS actually is connected to the Internet using IPv6 and it is not just for their own internal network and the packets actually get dropped at the edge.