Football shirts are a rip off IMO, as many, even the top sides, are just basic template shirts with a badge and sponsor logo stuck on. You can pick up unbranded Nike/Puma etc shirts very cheaply.
The business model for rugby is a bit different. Lower volumes produced and virtually all (at least the home shirts) are completely bespoke designs for the club. Like them or not, our Adidas home shirts are not copy cat shirts from other clubs. They're also better quality and more durable than football shirts. All adds to the cost.
I can just about justify the expense of a Quins shirt every 2-3 years and in general they have lasted well but would never get the shorts and socks as well and don't feel the need to replace it every year!