respond_with and ajax

Suppose I have this controller:

class SalesController < ApplicationController
  respond_to ???

  def get_price
    @price = Product.find(params[:product_id]).price
    respond_with ???
  end

end

1) What do I specify for respond_to() so that get_price() will accept
ajax requests?

2) What do I specify for respond_with() if all I want to do is return
@price?