I'd like to run some long-distance 3D HDMI and I'm looking to use CAT6 STP cable. Where is a good place to buy it? Monoprice has CAT6 UTP 1000 feet for around $100 (plus $30 - $50 shipping to the ...

Fiber is also a lot thinner than multiple Ethernet cables - you can get 12 strand OM3 cable that's about as thick as a single Cat6. This could be a factor, depending on your conduit capacity.