First I want to disclose I'm the owner of Pucon Kayak Hostel and acknowledge your mention of not wanting to pay for expensive trips. I've observed many nomadic travelers such as yourself with same skills and may have helpful advice.
A. Your request is a tough one with few that will reach out to help. Repositioning your request might help. Here's why.
Kayakers whom save up their annual harvests to reap rewards of kayaking in South/Central America are 95%+PLUS here to either go kayaking daily off waterfalls or super fun runs. Or they are like yourself and not good enough to do it themselves. And that puts them in that category of paying for the expensive trips. Basically, most of the kayakers I observe simply do not have the time to be helping likable class III boaters such as yourself.
B. You might be able to show up to a kayaker hot spot town such as Borja, Tena, Pucon, Maipo... and if you are charismatic find a floating guide to pay under the table for guiding. But you get what you pay for and you will discover there is something missing.
A big part of any of these trips is your community and the go kayaking from morning until night. Eg- PKH just finished our annual Claro trip and we were doing 6 am laps until dark at 8 pm. Group camp fires, high fives and Chilean road trips.
Hopping in with just a local guide or a floating kayaker may not provide the same experience for what you are seeking. Which should be to not only experience the local rivers but to vastly improve your kayaking skills, to run the rivers safely, find a community of friends and to explore the local culture.
C. Possible Solution 1: Can you organize 2 to 3 friends at the same level as yourself? There are lots of kayakers at your level. PKH would be happy to offer discounts to a group organizer such as yourself. This would help you earn discounts to the programs that offer the best experiences.
PKH just had a kayaker from Canada write to ask if he got 3 friends to come to our Road to Futaleufu trip, FEB 21 TO MAR 1, could he earn a DISCOUNT. Absolutely. What if you negotiated a group of similar kayakers and negotiated a group discount? Then advertised on the Buzz?
D. Possible Solution 2: Rent a vehicle and arrive to a destination. If you want to attract kayaker friends whom will teach you and take you to the rivers. Show up with a vehicle. Kayakers in these areas all have the same problem. Wheels & transport to the rivers. Show up with their solution and trade them transport in the mornings to the stouts in exchange for taking you kayaking and gas money. But renting a 4 door truck costs money too. Again, can you get friends to help with costs?
E. Possible Solution 3: Ask one of the expensive trip companies if you can pay for a trip and stay on for an additional month and volunteer work for room and kayaking. Winning a coveted job with one of these companies is challenging and the best companies have really great guides. Eg- PKH hires the best instructors from NOC Paddlesports. And I had over 40 applicants this year for instructional jobs. No one got an instructional job. Although, Carson Lyness whom instructs for Wet Planet arrived on an internship and has proven herself to be a world class instructor and asset worth investing.
You might just open the door for yourself by offering to pay for a trip and asking if you can stay on for a month +PLUS to volunteer.
F. Possible Solution 4: Volunteering. These days even getting a position volunteering is Challenging. The benefits go beyond daily kayaking. Purpose, community, shelter, transportation, equipment, and bonding are a few.
Pucon Kayak Hostel Employment Page.
Good luck Becca. Hope this helps.