Dave,I just checked my passport(glad I did because I found a £50 note and 2 thousand pesos I stashed for emergencies)my extension cost 3030 pesos,they asked how long I wanted,I just said "Give me a month more mate" which I got,dont know how long I would have got had I been a little cheeky,if you dont ask you dont get,but there was an immigration officer sitting on the seats customer side of the screen,Fixer?Who knows,its sometimes worth chatting to people like that