I don't have the hourly rates handy but they can vary a great deal from US20 on up, and up and up especially when dealing with a foreigner. Also, the PI's here have the reputation, justly or unjustly, of negotiating with the person being investigated to get more money than what the person who wants the investigation is being paid. Finally, Charles will be leaving the country soon so his services will no longer be available.
This is a good business opportunity for an expat established here with this type of background because there is definitely a need. As an example before the economy went South he had 3 or 4 cases a month at US500 to US1000 - not bad money. One of the most important components is hooking up with a local pi or someone to do the investigative work because obviously a gringo will stick out like a sore thumb. Contacts can be easily made at the "detective privado" licensing office in SD off of Charles Sumner Ave. near Pricesmart. Finally, this doesn't have to be a dangerous business if one limits oneself to investigating spouses or gf/bf. I would shy away from any business type of investigations for obvious reasons.