B&H now has multiple configurations of the new 27″ iMac with Retina 5K display available for pre-order. While the base model is only $2494, I think the one to get is probably the 4GHz Core i7 with 4GB VRAM and only 8GB RAM for $2999. Then pick up some aftermarket OWC or Crucial RAM for a fraction of what Apple charges. Check out all of the configurations here at B&H Photo.
If you’re a photographer trying to figure out if this iMac is worth here this article may help:
http://technologyformedia.com/2014/10/20/is-the-5k-imac-with-retina-worth-it-for-photographers/