Current DS games usually go for around 4,800 yen in Japan, which is about $58 USD, but DS games only cost up to $35 in the US. Given that ratio, we might expect to pay around $42 for 3DS games in the US (if the information, and our math, is accurate).
It's all speculation for now, but we'll know more about the North American launch after Nintendo's media event in New York on January 19.
[Source: Andriasang] GamesRadar]