There are a few options available in the aftermarket. I suspect your garage just doesn't want to sell one to you.
Broadly you have three options:
- Original VW - this is the most expensive and what it sounds like they want to sell you
- Aftermarket OEM spec - these are varying levels of quality. Try
https://www.autodoc.co.uk/ or
https://www.eurocarparts.com/ and put in your registration
- Aftermarket performance system - usually in stainless steel. These are generally louder but depending on what you go for will allow you to make more power later.
It sounds like aftermarket OEM spec is the sensible option for you. If you want an aftermarket performance system that is on the more quiet end, try the Milltek Resonated 2.75" system. Resonated is important if you worry about sound. Around £650 I think. Of course you could buy used too.