In many situations, the two phrases mean pretty much the same thing. In your example, they mean the same thing. Person pointing to a computer in a store: "How much is this computer?" Person then points to another computer: "What about that one?" Person then points to another computer: "How about that one?" "What about that one?" and "How about that one?" mean the same thing in this situation.

For spoken English, either expression is okay. There are many ways to ask about help with prices from a salesperson. Examples: "What does this cost?" "What does that cost?" "How about this?" "How about that?" "What is the cost of this?" "What is the cost of that?" "What about this one?" "What about that one?" "What about this one?" "How about this one?" "How about that one?" "How much is it?" "What is the price? "How about the price?" "What about the price?" "What price does it sell for?" "How much does it cost?" "What is the price?" "What do those cost?" "What do these cost?" Or, incomplete sentences like this: "...and the price of this? "...and the price of that?"