This is a good point. Limiting the free tasks could just mean that you use a second to-do app for tasks you don’t want to risk money on. It may not make sense to encourage that.
How about applying the same insight we had about freebees (embarrassingly still not implemented but it will happen!) and just default to $5 but let you change it to $0 when you create the task. (I also might argue for not letting you bump it up higher than $5 when first creating it. As in, you have to fail at $5 if you want to have $10 at stake.)
PS: I see you reached a similar conclusion while I was typing this. (: