In conversations with teachers, the two sites I hear Yacapaca most frequently compared to are SAM Learning and Boardworks Doddle. The three sites are very different in both function and ethos and most schools probably use at least two out of the three. However, to the extent that a student who is using Yacapaca is not at that moment using either of the others, we can be said to be competitors.
So how do we stack up? In the following chart I have used as far as possible data published by the companies concerned and up to date as of June 2015 (prices to April 2016).
Yacapaca 