One other difference between Microshift and Sunrace that I failed to mention last night is the lack of a barrel adjuster on the Sunrace shifters. This is not a big deal for the indexed one, as the derailleurs I use have barrel adjusters...and one could always run an inline adjuster if needed. Still, it is nice to be able to tweak the adjustment while riding if needed.
I, too, cannot understand why the Microshift thumb shifters are so expensive (especially when compared with other shifters of much greater complexity). I can only guess it's an economy of scale thing -- thumb shifters likely don't sell in large quantities and they're probably more of a niche product. Having said that, they do work very nicely, and their build quality is very good. I guess that costs money.