Gotta say from experience that dealer fitted wheels / tyres is not the way to go. I've got two sets for my Cooper.
Looked at getting 17" R90s and got the same $5.5k quote, then ducked around the back to their spare parts section and priced up a set for $1600 plus about $800 for tyres from a local supplier.
And you can't tell me that there's $3000 labour in fitting a set of wheels to a car!