Now that the ISS has the capacity for a larger full-time crew, the seats are more likely to be devoted to long-duration ISS crew rotation than short-term ISS visits, whether visits by professional EU / US astronauts or folks flying privately. I’ve no doubt that there are economics attached to the Russian seats that are similar for both cases – the EU and US have to pay for the lift just like us ordinary folks.
There are a couple of interesting twists to the story.
One is that, when the Shuttle is retired, the Russians will have the only manned access to orbital flight in the ISS partnership. Russia and China will be the only nations with manned orbital capabilities, and the US huffishly refuses to welcome China into the ISS club. Expect the price of a seat to rise substantially while that’s the case.
Another is the EU’s plan to evolve their autonomous cargo vessel (ATV) into a manned capability, something that’s perfectly feasible and quite sensible IMO.
And the third twist is that the Russians have long been open to commercial offers for a long-duration flight (six month ISS crew rotation). That woudl require substantially more training (12-18 months minimum depending on who you ask) but would certainly include the Soyuz lift to get there and back.