I don't actually remember. I used to set all my settings to US/American ones because some apps were only in the US app store, so there's a good chance I was looking at the US$1 price. Not sure what my friends saw in the Brazilian app store.
I think it was R$1,99, that was not exactly US$1 (even considering the stronger Real in the period), however it was not exactly equivalent to US$1 either.
In many countries, WhatsApp is the defacto communication platform for businesses to communicate with customers.