Has anyone joined a Panama Canal tour outside of the cruise ship?

[i<3cheesecake]

I'm going to a Western Caribbean cruise with Carnival cruise lines this upcoming August and am stopping by Colon, Panama. I was wondering if anyone was able to find a Panama Canal tour outside of their cruise line (we're not sure if there would be locals standing outside advertising their tours as in other ports) as joining with Carnival is quite pricey (almost $200 per person) and we have quite a large group. Any info would be great, thanks!