i18n lambda + using view helpers in error messages

en.rb

# config/locales/en.rb
{
  :en => {
    :activerecord => {
      :errors => {
        :models => {
          :bid => {
            :price_too_low => lambda { |errors,attributes|
              helpers   = ActionController::Base.helpers
              currency  = attributes[:price] || 0
              formatted_currency = helpers.number_to_currency(currency)

              "Your bid must be greater than #{formatted_currency}"
            }
          }
        }
      }
    }
  }
}

example.rb

bid = Bid.new
bid.errors.add(:base, :price_too_low, :price => 123.45)
bid.errors.full_messages # => Your bid must be greater than $123.45