I see quite some time has been devoted to this subject. The first time I read the hairdresser example, the English struck me as quite wrong. I would add my two cents as follows:
If I went to the hairdresser, I'd spend a lot of money or If I went (had gone) to the hairdresser, I would have spent a lot of money.
Those seem to me to be the simplest way to correct it because one can't correctly say I would spent.