I bought a Champion Polyester 6 oz wind-shirt at Costco for about 10 dollars. It was too breathable, and had either no, or very crappy DWR.
Easy fix on both parts. Washed it well in hot water with oxy clean (in case it had any DWR), rinsed very well. Took some silicone adhesive, thinned it a lot with paint thinner, mixed it up very well with an old hand held blender i don't really use anymore otherwise (it's now dedicated to this function).
Threw the windjacket in the dryer to get it nice and hot, and applied the silicone adhesive with a combo of foam brush and microfiber cloth on a hot day outside. Let it dry outside, then put it in the dryer again.
Now has a more reasonable wind resistance, and a great DWR, which i think will last a long while (perhaps similar to EPIC). In any case, it's a much thicker coating than most diy, pre made type DWR treatments.
This process can be applied to any polyester or nylon fabric provided you get rid of any pre-existing DWR, and the material is breathable enough to begin with. Don't add it to a fabric that is already highly wind resistant–you'll basically make a silnylon or silpoly fabric, but likely not as good as commercially available stuff.