Udon price

The average cost of a bowl of udon in Tokyo is typically around 700-1000 Yen, which is about 6-9 USD depending on the exchange rate at the time. More exclusive places can charge higher prices, of course.

Concerning the structure of your question, indeed it can sound more natural in spoken or written English. Here's an example:
"Imagine you're in Tokyo, and you decide to eat a bowl of udon. On average, how much would it cost you?"
Or,
"If you were to visit Tokyo and decided to eat a bowl of udon, how much would you expect to spend on average?"