Yes Astrophotography is usually expensive, but like anything else, you can do some things a bit cheaper. As metioned to do star trails all you need is a fixed tripod and a caera that allows the shuuter to be held open for long periods.
Another option is to buy a simple EQ mount, a basic scope, piggyback a camera with a 50mm prime lense and learn to hand guide - very cheap and can produce interesting widefields, but you have to be prepared to spend a lot of time hand guiding in the cold dark night
For most imaging work a good mount is essential and the minimum would probably be an EQ6 Pro style mount which is going to set you back $1500+, add to that a scope, guidescope, guide camera, software, laptop, cables, adaptors, focusers, power supplies etc.... and that assumes you are using a DSLR as your camera. If you get dedicated astro cameras they start at around $2000 and head north from there and may also need filters and filter wheels.
Best advice is get the biggest dobsonion you can afford and handle, enjoy it and if the astro bug really bites then have a look at imaging.
Malcolm