Purchasing an astrophotography mount

I do some astrophotography for fun in my spare time. I'd like to get into doing deep sky photography. In order to do that, I need a moving mount that can keep the camera aligned with the stars for minutes to hours at a time. I'll be using (at least initially) a Canon 7D (original version) with Canon lenses rather than a telescope. I currently have a 200mm lens with 2x extender, which makes it 600mm equivalent on that body.

I'd like to know if others here have ever done this and what type of hardware they've used for the motor and mount? Prices seem to be all over the place and options vary greatly on different devices. For example, I see the following:

Sky-watcher EQM-35 - $623.00US - Seems pretty full-featured for the price, as it includes tripod, motorized mount, alignment scope, and database of astronomical objects.
Celestron Advanced VX Computerized Mount - $899.00US - Seems very similar to the above, but does not include a scope, but is ~$250 more
Orion AstroView EQ Mount & EQ-3M Motor Drive Kit - $269.99US - Like the first one, but without the scope and holds less weight, and no database of objects to look at

I get the difference in price between the first and last, but not the middle one.

In any event, curious if anyone has used any of the above or any others and what their thoughts are on the quality of different brands, and anything I should be looking for or avoiding.