You have to keep your eye out, but it only took about a month of looking before I saw this PB1400 on eBay. It didn't have the highly desirable higher-end Sonnet accelerator, but just going to G3 is pretty good in and of itself in terms of one of these older machines--as large a jump as 386 to 486 or 030 to 040 I'd say. I have to admit that if you're longer on cash than time or if you're in a bad spot geographically (probably not a lot of old high-end Apple equipment floating around garage sales in Quincy, Ohio, for example), eBay is your option of first and last resort. It went for just shy of $50, and had the RAM to boot, but I think folks were put off by the bezel being broken and the lack of photos and detail.
Best,
John