I took the full day Elephant camp, rafting, ox cart tour today. I was a bit dubious that I wouldn't do the elephant permanent harm, but the booking agent said no problem.
Even though I had been up with Ern until 3am or so, I got up at 7am and got ready for the tour. I'm sure most of you Chiang Mai veterans have done it before. 800 baht from 8:30am-4:00pm.
The elephant riding was the most fun, about an hour or so. I really thought either I or the elephant were going to fall down/off. It worked out fine though, and was a bit of a hoot in reality. I guess I'm easily amused.
Expect to spend 100-400 baht additional in bananas, sugar cane, photos of you and your noble steed ("You hear that Shrek, he called me a noble steed"!), plus tips to drivers, etc.
You get a decent buffet lunch, and after the lunch, it's pretty much taking you to the Elephant dung paper maker, Orchid/Butterfly farm which is just trying to sell you stuff. (To be honest, most of the tour is about selling you stuff, but you get a lot more value out of the Elephant, rafting and ox cart parts.)
It was interesting to see locals wading into the river to sell you hats and trinkets. Even lowering prices when you're about to float away. On the oxcart trip, one little 5 year old girl chased after a cart in front of me for about 200 meters, trying to get them to buy something. They finally bought a couple of bracelets. That kid is a born salesman!
Even though it's a bit hokey, and we can talk about chaining up Elephants and other cruel things, it was worthwhile in my view. I think you can just ride the elephants if you want. I was quoted 500 baht an hour, so that might be another option.