Hi Andrew,
"Spend as little as possible" and deep space astrophotography don't really mix
The EQ6 would be the best of your three options, especially if you are interested in astrophotography with a reflector. Bintel/Andrews has the EQ6 new for $1799, so if you can get it for $1336 that would be a great price. They occasionally come up in the classifieds section here on IIS for around $1000 - $1200, but usually get snapped up within a couple of hours.
You may find imaging a bit tough with an SCT+DSLR as your first scope/camera kit, due to its long focal length (difficult to get round stars) and the long exposures needed.
A small refractor such as an ED80 would be the easiest way to get started, learn how to set up the scope, align accurately, get autoguiding working well, etc. It would also frame many of the bright nebulae quite well. You can also do some great imaging with your DSLR lenses too.
Hope that helps!