That seems a good price for what you have ended up with.
I built a 3m x 2m from scratch, using insulated panels. By the time I put in a base, drain, erected the panels, installed overhead rail to take weight of internal rail, chiller unit and internal rail, it cost me about 7k. Ive ended up with what I wanted, but not cheap. As someone has said, go for a ceiling height that gives plenty of room. I went for the 2.4m high panels, which seems alot, but by the time you have your rail and gambrel hanging down, you've lost quite a bit of height. On mine, a big stag will just clear the ground .