I do the same type of calculating for recreation like you're talking about.
As a family we decided not to join a pool b/c of the way the costs amortized out. (costs range from $400-800 a season for a family plan) We'd have to go every day for several hours to make it worthwhile and I'm just not a sit-by-the-pool kind of gal. The $30 baby pool from last year suits our needs just fine for this summer and we can alwyas pay a guest fee and go to our friends swim clubs.
I do this with just about all activities. We're going to an amusement park this week, $90 admission for 4 people but it's a once in a summer thing. I have fond memories of going to amusement parks as a kid and I want my children to have the same opportunities. That's a splurge for us.
Swim lessons equal out to $12 a half hour but it's teaching safety as well as fun so it's money well spent. Ballet lessons are cheaper but you have the cost of recital costumes. Then again, after the recital the costumes go in the dress up chest and are always a big hit at playdates.
We have little recreation without our children and when we do, we go out to eat. But we ask for gift certificates as gifts so that usually costs only a tip. Our netflix subscription was a birthday gift from a family member. Also, when asked about gifts for the kids, I suggest a few people go in together and get gift certificates for things like lessons, admission tickets to places like the Zoo etc. This only really works with family but it has cut our entertainment bill considerably. (also keeps a lot of toys out of the house)
Funny you should mention a pool, as we join a local pool (outdoor, so summer only) for around $300 and get huge value out of it... My wife and four kids go there to swim daily, and I accompany them on weekends and the occasional evening. If I were to work out an hourly rate, I guess it would look something like this:
5 days/week x 4 weeks/month x 3 months x 2 hours/day x 5 people = 600 person hours
3 days/week x 4 weeks/month x 3 months x 2 hours/day x 1 person = 72 person hours
$300 / 672 person hours = $0.446/person hour
Of course, I'm spreading that across family members, but if scale back up to the cost of a trip for the whole family (all six of us, two hours) we're still looking at under five and a half bucks for two hours of fun and exercise.
But I don't generally scale things like this.
JD: If you really enjoyed it, I can't believe that you'd limit yourself to once every 5 years given the relatively low cost. Would it kill you to blow $80 every year for something you seem to really like doing?