いくら・いくつ

いくら asks a price or an amount of money: これはいくらですか, "how much is this?"

いくつ asks how many, for things counted with つ: りんごはいくつありますか, "how many apples are there?" It also asks age, politely: おいくつですか, "how old are you?"

For things with their own counter, 何 goes in front of the counter instead: 何人 (how many people), 何本 (how many bottles), 何枚 (how many sheets).

Mixing up いくら and いくつ is one of the most common first-trip-to-Japan slips, and shop staff will usually understand anyway.