Yes, cost is the problem- and I dont know what to look for. :/I haven't read all the posts but I thought I would contribute some thoughts. Apple vs Windows is a bit like Canon vs Nikon. The bottom line is that is down to personal preferences and budget.
I think that possibly the choice is more Windows vs Unix/Linux. First let me declare that I have Windows XP and Linux running on my personal computer. I believe that Unix/Linux is by far the better operating system. I cannot give you black and white facts. All I can say is that Linux/Unix gives the user a far better experience of using a PC. As Apple is a Unix based system then that would seem to be the better choice. There also seems to be some thought that Unix/Linux is less prone to virus attacks.
But, there always is a but, in the UK I think that entry cost for Apple is around £1000. There doesn't seem to be much of a secondhand market either. So, in terms of cost you can certainly buy Windows based systems for at least half that cost. If you went down the Linux route that offers more options in terms of choice of machine. While there is a huge repository of 'free' software for Linux, the downside is that a lot of the major software suppliers like Adobe don't produce software for Linux, which is rather odd as they do for Apple which is Unix based system! So for image processing you have to take that into consideration. If you chose Linux, are you prepared to accept the 'free' software options or do you want to access all the major image processing software? If you are currently using Windows then if you switch to Apple there is also the additional cost of having to buy software that will work on the Apple machine. There are 'virtual' machine options but that will only confuse the choice!!
I can hear people snoring!!! so I will sum up.
If cost isn't an issue I would certainly look at the Apple option first. If cost is an issue then I would go for a Windows based system. Either of these options gives the potential to able to install the major image processing software e.g. Adobe based products. By choosing the Windows based option that could still allow you to have a Linux based system as well which could give you the best of both worlds.
Cheers for now
Gary