Yikes thats a rip off. I used to work designing custom closets. When we bought this house I new I wanted them. We used Home Depot's Expo (their high end design store), who contracts out with a closet design company. We paid $1,200 for our walk in closet with a total of 6 drawer units (many, many drawers), 3 hanging areas on my side, one long one on dh's side, and number of shelves and a 2ft wide (by 9ft tall) shoe wall with a removable hamper at the bottom. We also did each of my kids reach in closets for a total of $800. Each has 2 hanging areas on one side and 2 two drawers units (total of 8 drawers and 2 shoe shelves), and 4 shelves on top of that. We then did our home office which is a 10x10 room. It has 3 desk areas, storage drawers, and cabinets on 3 of the walls (including one that runs floor to ceiling to hide all our networking components), with the design on the doors, lol, and a of course the wrap around desktop. We also paid a bit extra for moulding on the cabinet tops and a special thing underneath the desk that hides all the wires. Grand total for office: just under $4,600.
Like I said I used to work in the business, and I knew which upsells really did benefit you and which just money down the drain. But if I were you I would keep looking. The nice thing about going through Expo is even though they contracted out the work Home Depot stood behind it. We had one problem with a drawer and Home Depot immediately stopped payment to the contracter and held it till they came out with a new drawer. Btw these were installed by them (included in the cost) but I have installed closets before and if you can use a drill and a level you can install a closet.
edit: okay don't know how my ticker got all screwed up hmm... and I didn't see the size of your closet. Wowza thats big. Ours is about 9X6 with some weird little areas where its deeper and some where its shallower. Depending what you are looking at I could see it getting up that high. Try looking at easycloset.com and entering your design into their online planner. May come out cheaper to order through them and hire a local contracter to install it if you really don't want to (but trust me its not that bad).