Magkano?
How much? (the price, not the amount)

Gaano...?
How...?  (the amount, not the price)

Gaano karami ang kailangan mo?
How much do you need?

Magkano ito?
How much is this?

Magkano iyan?
How much is that?

Sampung piso.
Ten pesos.

Ang mahal.
How expensive.

Wala bang tawad?
Isn't there a discount?
(used in haggling down the price)

Magkano daw?
How much did she say it was?

Iyan ba ang pinakamura?
Is that the cheapest one?

Tanungin mo kung magkano.
Ask how much it is.

Tinanong ko kung magkano.
I asked how much.

Tinanong mo ba kung magkano?
Did you ask how much it was?

To ask how to do something, use the word paano.

To ask the amount of something, use gaano.