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I second the Both option. No need to go to Mexico for Nitrox. I paid $75 for mine and it was maybe a 2 hour class after doing the bookwork at home. While it may be a placebo, many divers, including us, feel much less tired after dives on Nitrox. The "nitrogen naps" are much shorter after lunch.
Rescue was the class that I felt like I was becoming a diver. (I'm still working on it...but I'm much closer than I was three years ago) If done correctly, you will be spent when it's over. I'm not sure I would want to take the course on vacation though...but that's just me. I may have paid 150...maybe 225 for my rescue course. Friday night was book work. Saturday was rescue, Sunday was search. At least 6 dives. Again, great course, but I would do it before a vacation.
Good luck, safe travels.
Jay
I She was spent. But likewise, had never seen someone so happy after completing a dive course.