Grannyring, the computer is unlikely to have a big impact on sound quality as long as it meets certain minimum performance standards (though there are things you can do to make your computer "sound better"). So, yes, there are cheaper ways to go than the MacBook Pro. It doesn't even have to be a laptop -- I use a Mac Mini as my audio source, and then control it remotely through a laptop, but there are other remote options. You can also use Windows computers. I don't know much about them, but many people have good results with them. You may even be able to do a trial run with your current computer.
If you really are thinking of jumping in, and are new to the game, I'd suggest reading the computer audio set up instructions on some web sites (both Ayre and Wavelength have them, but they can be found elsewhere). When you have a better idea of what you want to do, post your intentions and questions on the PC audio forum here, or on a forum at Computer Audiophile -- you'll get lots of tips and suggestions from experienced users. Good luck!
If you really are thinking of jumping in, and are new to the game, I'd suggest reading the computer audio set up instructions on some web sites (both Ayre and Wavelength have them, but they can be found elsewhere). When you have a better idea of what you want to do, post your intentions and questions on the PC audio forum here, or on a forum at Computer Audiophile -- you'll get lots of tips and suggestions from experienced users. Good luck!