Many of the apps I downloaded were free, however those that were available for purchase were very affordable. The most expensive one I found was $4.99 and the cheapest one was $0.99.
My favorite ones are:
Italian Cards (free app)
Feed Me Pencil Bot (available in Russian, French, Spanish, Chinese, Japanese, Arabic, German, Italian and Korean) $1.99
I will add more as my kids and I try them! :)