Let's face it, nothing in photography is cheap. However, time lapse is still one of those things that can be done on limited resources and with software that already comes with everyones' computer.
The more expensive solution, for me at least, is the Canon TC-80N3 intervalometer shown below. As a side note...it is Christmas and it's not too late mom - just saying. These devices go for about $145 new and act as a time lapse control for your camera with a direct connection to the shutter release port. If you're serious about time lapse, you buy one of these.
Now if you're just interested in time lapse, but don't want to dole out the cash there is a cheaper method. Every Canon SLR camera comes with a piece of software called "EOS Utility." When connected to a camera there is a selection available for "Camera settings/Remote shooting."
After you select that option there is a camera control window that comes up. For night time shooting I generally set my camera to small raw output, lock the white balance to "daylight", lock the aperture, lock the lens to manual focus, and use manual mode. Despite what the window shows below, I actually shot the sequence at ISO 1600, 15 second exposure, f/2.8, and manual focus. In the middle right of the window you see a little clock icon button. Click on that.
This brings up a limited time lapse control feature; not as full featured as the intervalometer. You have to be tethered to a computer during the entire shooting sequence, but it does work as long as your laptop and camera batteries keeps going. Note that you can do bulb or interval shooting, however the interval shooting is limited to a 30 second exposure so you can't do 2+ minute deep space exposures. As recommended on timescapes.org, I set the exposure time to half the frame interval; i.e. exposure is 15 seconds so the interval is 30 seconds. This is an optimal setting for later turning your time lapse into video since video cameras typically use a 180-degree shutter angle (in normal 24p a frame is exposed for 1/48th of a second).
As for turning the pictures into video I used Premier Pro, which is slightly overkill but I'm comfortable using this program. Clarence has successfully used Windows Movie Maker ( my face grimacing in pain at the thought) with the results included in my previous post about time lapse with the Pentax K-5. iMovie works equally as well. You just need to be able to drop the pictures into a sequence with each picture representing one frame of video.
Below is just one of the frames of our setup. You can see the 5Dm2 and 7D on tripods, with my camera tethered to a laptop on the passenger seat via USB cable. No, this isn't HDR, just a long exposure at ISO 6400 on the Pentax K-5. You gotta love the lens flair from the moon on the upper left.
Finally, the short video we produced. It's not anything ground breaking - just a bit of experimental fun.