Hello Cameron,
I share Dan's comments, and I feel he is being as polite as can be in his reaction to what many would consider to be an almost unbelievable quote!
Question regarding whether you can get this done at a non-Audi garage is I think answered by yes you can, providing the approved "parts" are used by the (VAT registered) garage doing the work and they provide you with receipts for the parts and work done.
If it were mine, I would first follow Dan's advice and get an alternative quotation from another Audi dealer. My suspicion here is that you might be assuming it requires an oil (and filter) change whereas the car is due for a service, and they have quoted you for the service and not simply just changing the oil and filter.
Let us know on that Cameron, and if indeed you are correct with this charge for simply changing the oil, then we can advise you what options you have from there. No point in going through it all until this bit is clarified.
Kind regards,
Gareth.