I know the HG is the MAC 187, but who has $42.00 to spend on a brush?!
Fear not...i have some real dupes for you all.
Dupe #1: E.L.F. Studio Powder Brush ($3.00) (read review here)
The brush is very dense and rigid enough to do the job of a stippling brush and the job of a flat top kabuki brush, that provides full coverage. I love that brush! I have had it for a year; no shedding or bleeding. I just use baby shampoo to wash it. Nothing fancy.
Dupe #2: Professionnel Platinum Stippling Brush #44 ($35.00)
This brush is probably the closest one to the real thing. It is very soft, gets the job done and gives you the airbrush look, which is why everyone is going crazy over stippling brushes. However, it is only a $7.00 difference...but hey, its still $7.00 :)
Dupe #3: Sigma Duo Fibre F50 ($16.00)
I have heard good and bad things about this brush. My overall impression is that it does what the MAC 187 does, at a fraction of the cost, is very soft, dense, not floppy (like the E.L.F Stipple Brush-read review here), BUT..it sheds and has a residual scent. If that doesn't bother you, go for it! I have also noticed that not all brushes are made equal, especially the lower end ones. You might get a brush one time that works amazing and if you go and buy another one, exactly the same, it might not work as well as the first. If it were me, i would buy it and try it out. Has the most potential (other than the Sephora, which is still pretty pricey).
Hope that helped.