A strut can make that kind of noise but a sway bar could also do the same thing. So could a dry ball joint or tie rod end.
I think you’re confusing shock and strut. A shock is usually cheaper but still way expensive on an Audi. A quick look shows shocks at about 130 each and most car parts houses do not even list struts as being available.
An on-line look shows struts, NOT shocks, at around 400 to 500 bucks apiece; and yes, they’re always replaced in pairs.
Ouch. Welcome to the Audi world.