What radio problems are you having? Is it definitely the head unit, or might it be something else, e.g. aerial, speakers etc?
If you're after a brand new like for like replacement unit they can be expensive if purchased from VW. Many cheaper options available from the likes of Halfords if you're after Bluetooth & aux in, but you will lose OEM appearance.
If I remember correctly, yours will be an RCD210 or RCD310 unit. EBay will have some used and reconditioned, perhaps the odd brand new one, but beware units with dubious sounding origins or fake looking units from places like Hong Kong, China etc.
The only compatible VW units can think of that had Bluetooth built in were the RNS310 & RNS315 units that also come with sat nav, but they can cost mega money.
Maybe try places such as Hazzydayz or Advanced in Car systems as a bit of research.
Good luck.