I would suggest getting a hold of Gian Marco Vaullentino who runs Cusipati, a rafting company in Arequipa. We did trips with a little of his help down the colca and cotahuasi, which are both totally awesome I would reccomend them both. im not sure how confident you are in your mini me skillz but the commercial sections on both rivers are somewhat challenging, mostly class IV/IV+ with a few class Vs and I think that the colca was the only one with portages, they kind of suck. i can give better beta if you want. the access is quite easy, both put in towns can be reached by bus but then require full day hikes to get to the river.
THe apurimac is a must do, can also link up with the less run upper black canyon section but it doesnt have too much whitewater and lots of sand fleas. The commercial section is a blast and wow, really pretty.
Ask gian marco about the area around macchu picchu where he has bought property,there is abundant day trips out of there.
In Cuzco his brother Piero is the contact at terrexploradora or whatever. Both great guys, can help with logistics and equipment as well. pm me if you want more info, i was there for two and a half months last year and it is the shiT!