You're on the money there Marty. BYE and APT are similar applications and do the same thing. I'd happily use APT but I've already paid for BYE and I'm happy with that too. They are not hard to use once you understand some of the terminology.
The next 'best' Canon model in the newer offerings for astro is the 1100D (or it was) as it is a very low noise sensor. Same sensor size (12.2m) as the 450D but newer technology. Nonetheless it is still better to capture real photons at lower ISO's than push the ISO up to using gain to simulate photons. It will still introduce more noise to some minor extent. There is a lot of info put together by more erudite people who have tested and documented the results on various cameras, sensors and their settings.
I got my 450D cheap because it had a small problem but astro use doesn't need that function. My next purchase I hope, will be an 1100D, not because it will be faster but because it will have less noise at 800 ISO.
What you are looking to do is get the best signal to noise (S/N) ratio possible. Most of what you are imaging is invisible to the human eye and only marginally brighter than pitch black so that is the critical factor. The better that S/N ratio the more object photons (Signal)you will capture compared to empty space photons and pixel noise. Again this is documented by a number of experimenters.
In the meantime use anything you have to learn and experiment. My first were with what is now my guidescope, an 80mm f5 Achro using my old Konica Minolta 7D (6m) on a modified EQ2 mount ( with a brick hanging underneath to steady it!!
). With a CLS (ClearSky) filter I got quite acceptable Lagoon and Trifid images in my early attempts.
That is when you start learning and start spendi.... err growing your knowledge and expertise. I've still got a long long way to go and I'm enjoying the journey at every step.