In the US: USD$100 (GBP£52) for an upgrade to Basic, and $250 (£127) for an upgrade to Ultimate.
In the UK: £100 ($196) for an upgrade to Basic, and £250 ($490) for an upgrade to Ultimate.
Right, if I ever get Vista I'll import it from America. The pound is worth nealy two dollars, not one. And Microsoft can't blame international shipping for this - the UK has no shortage of CD and DVD stamping facilities.