@gromit - one of the reasons that it is thought that May 5th next year will be chosen is thats because thats the date of various local and council elections, so is a method of ensuring a higher turnout than might otherwise be the case.
As to its worth - well that depends on whether or not you think the existing first past the post system is a system that is both fair and allows voters to feel that their vote counts, that it matters. For a huge number of voters, that is not the case at the moment, so some form of PR would be preferable. Given that any change to the voting system is likely to be around for a while, £80,000,000 doesnt seem that unreasonable to me.