Um...overall, probably around £20. Exchange rates don't seem to affect it, something else does, meaning that PC gains much less money than I lose.
I don't know when I did it...I think I bumped myself from Tier 2 to Tier 3 this year, from Tier 1 to Tier 2 sometime last year, and probably got Tier 1 a couple of weeks before that. I've been a supporter for a whole year though, I think.