Skt 939 was a handy way to get the last tour of duty out of your old DDR1 memory with the fastest CPU possible, for cheap. $100 I know seems high but there's supply and demand of course.
I can't see the logic in thinking 939 had most of the performance as an equivalent AM2 platform, since you'd have to contrast the latter CPUs available for 939 at high cost, versus earlier AM2 or later AM2 at very low cost. Really no contest, last AM2 board I bought for $50, CPU for a little under $40, o'c it to 3GHz and called that great value... because lots of people really don't need uber-performance, just a solid quality set of parts at the lowest cost. Last 939 CPU I bought (before switching exclusively to newer platforms) was higher priced, single core, also o'c to about 3GHz (both conservative o'c). Sold that system to a friend a few years ago and he's quite happily running mostly single-threaded apps.