Answer:
How to say "How much does this purple bathrobe cost" is "cuánto cuesta esta bata de baño morada"
How to say "It costs" is "Cuesta"
How to say "They cost" is "Ellos cuestan" for male, this is for woman "Ellas cuestan"
How to say "Gift" is "Regalo"
How to say "For whom" is "Para quien"
There you go.