I agree: it is a fascinating subject and it doesn't
have to be mega-expensive to get started.
There may be some confusion about what I mean when I talk about the camera being at the "prime focus". When I use that term I mean that the camera is attached to the telescope in such a way that the image from the telescope's objective (main) lens is falling directly onto the camera's sensor. This is illustration (1) on the TeleVue™ Imaging Methods
page. In fact, all the methods described on that page concern various ways to use a telescope to produce an image on a camera's sensor but then TeleVue™ are
The cheapest way to start is to use the kit you already have. Have a look at Gordon's article Easy Astrophotography with normal DSLR equipment
to see what is possible together with some excellent advice on how to achieve good results. Even here in the Northern Hemisphere the Milky Way is putting on a reasonable show if you can find a location with dark skies. Use the fastest aperture you have and a high ISO. As the camera is unguided use the widest field of view to minimise the appearance of star trails. Be patient because, unless you are very lucky, it will take a few practice shots to get the manual focus right.
I mentioned "star trails". You don't always have to avoid them. To see what I mean have a look at some of the images from this Google Images search
If you want to take the next step up you still don't have to spend a fortune. I will quote one example from one UK retailer - N.B. I cannot vouch for the telescope. You can buy a small telescope on a motor driven mounting for £180/€270/$360 here in the UK. For product details have a look at this page
. You would need to source (or make) a suitable adaptor to fix your camera on top of the 'scope and then you are set to go.
If you want to buy even a small telescope I seriously recommend using a specialist company owned and/or staffed by knowledgeable amateur astronomers who will make sure that what you buy is suitable for your needs. A good company knows that you are likely to come back in a few years for an upgrade!
Finally, don't get bogged down by the detail of all this. It is also fun just to get outside during a crisp clear night. Forget the camera, find a location with no nearby street lighting, take a good pair of binoculars and a comfy chair and lay back and wonder. Oh, and make sure the neighbours know what you are up to!