The difference was that the Mac shipped with WYSIWYG editing software (MacWrite and MacPaint) that was so obviously better than anything on the IBM that it was a no brainer. People wanted them very much, but most of us simply couldn't afford them.
In addition, desktop publishing was a stupidly obvious killer app on the Macintosh (Fat Mac plus LaserWriter plus Aldus Pagemaker) and you could make your money back within a couple of jobs given how much money you would save.
Even a $400 computer was a huge stretch for them. It was possibly the absolute best purchase they ever made for me as it sent me down the tech path, but they thought VERY long and hard about it.
A standalone Sun-2/120, with cpu, 1M of memory, 42MB hard drive, tape interface, ethernet interface and software, cost $16300 in 1984 dollars, over 45k today.
So yeah, Macintosh was cheap