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The challenges in deep space astrophotography are the faintness of the subjects and the motion of the earth. Long exposures (typically from 1 minute to 10 minutes or so with a DSLR) are needed to capture enough light from the faint subjects, and that means it is necessary to track the apparent motion of the sky as the earth rotates. Even at normal camera lens focal lengths, you can't expose for one minute without the stars trailing, and using a telescope compounds the problem of course due to the longer focal length. At 1000mm, a one second exposure without accurate tracking will display star trails in a DSLR image.

What this means is that the mount is much more important than the telescope. The mount needs to be a sturdy German Equatorial Mount (GEM), with a well-engineered motorized drive train. I don't know if they meets your expectations of "reasonably priced", but mounts in the $1000 to $3000 range (new) are pretty much the starting point. With focal lengths over about 600mm it will probably be necessary to guide the mount with a separate guiding camera, so a mount with a computer interface is a must. Examples of entry-level GEM's capable of guided long exposure imaging of deep space objects at focal lengths up to 1000mm or so are the Orion Atlas, Vixen SXD, and Celestron CGEM. With lighter telescopes under about 700mm focal length, the Orion Sirius and Vixen Sphinx are sufficient.

For deep space astrophotography, you will want a telescope with a fast focal ratio, faster than about f/7 preferably. Most of the reasonably priced telescopes suitable for deep space astrophotography are newtonian reflectors and semi-apo refractors. A 2" focuser is just about mandatory for deep space imaging. Reflectors have the advantage of lower cost per inch of aperture, but larger aperture means a more substantial mount is needed. Look at the weight of the telescope optical tube, then look for a mount rated at at least double that value.

Stay away from telescopes and mounts with brand names you have never heard of and for which you can't find any objective reviews online apart from the vendor's site. If the price looks to good to be true, don't waste your money.

Many people get their feet wet in deep space astrophotography using normal and wide angle camera lenses for wide-field images of the Milky Way and some of the larger deep space objects. In fact, some people keep going with this type of astrophotography and produce truly stunning images any astrophotographer would be proud of. The equipment needed to get started with this kind of imaging is less expensive and more portable.

I'm sure I didn't cover everything, perhaps others will join in.

Don