Asking How Much Something Costs

You see something you like at a market stall and ask the vendor for the price.

You
Disculpe, ¿cuánto cuesta esa mochila?
dees-KOOL-peh, KWAHN-toh KWES-tah EH-sah moh-CHEE-lah?
Excuse me, how much does that backpack cost?
"¿Cuánto cuesta?" and "¿Cuánto vale?" both mean "How much does it cost?" and are interchangeable.
Vendor
Esa cuesta doscientos pesos. Es de muy buena calidad.
EH-sah KWES-tah doh-see-EN-tohs PEH-sohs. es deh mooy BWEH-nah kah-lee-DAHD.
That one costs two hundred pesos. It's very good quality.
You
¿Y cuánto vale aquella de color azul?
ee KWAHN-toh BAH-leh ah-KEH-yah deh koh-LOHR ah-SOOL?
And how much is that blue one over there?
Use "ese/esa" for things nearby and "aquel/aquella" for things farther away. It's like "that" vs. "that one over there."
Vendor
Aquella vale doscientos cincuenta, es un poco más grande.
ah-KEH-yah BAH-leh doh-see-EN-tohs seen-KWEN-tah, es oon POH-koh mahs GRAHN-deh.
That one over there is two hundred fifty, it's a bit bigger.