Best way is probably something like an arduino nano, sd card + slot, then just plug the sd in the computer and read your data, you probably could do the whole thing for 30$, and the time would depend on the size of the sd card
say you get a 2gb card which is like 2.1 billion bytes or something like that, and every event is something like
3/30/12 12:07 off,
3/31/12 14:08 on,
So that'd be about 2147483648/16== 134217728 events which I think if it switched every minute it'd last you 255 years, longer if its not done every minute, assuming if my math is right,
but at that point I think you would need a more accurate clock to be even close to good