How do you add Bluetooth to a C240/ 2004 no phone installed. Don't want to spend too much if possible!

How do you add Bluetooth to a C240/ 2004 no phone installed. Don't want to spend too much if possible!

The car I just purchased  (2004 C240) has a telephone feature on the steering wheel, but I am told it would cost $400 to install a factory Bluetooth component to allow the use of this feature.  Are they crazy???  

 

Someone please help!!!!!!!!!

Array ( [domain_id] => 1 [subdomain] => www.mbca.org [sitename] => MBCA [scheme] => https [valid] => 1 [weight] => -1 [is_default] => 1 [machine_name] => benzowners_org [path] => https://www.mbca.org/ [site_grant] => 1 )