I'll tell you what I have been doing...I started buying Whey Concentrate again from TP. It hasn't made one bit of negative difference compared to when I used isolate. I don't get the bloats and shits everybody complains about, and I mix it with 8oz of 2% milk every time. It has a few grams less protein, but I don't care for the price. I used whey conc/iso blends all the time in the 90's and early 2000's (ie Designer Protein, etc) and i never had issues. I went to Isolate when TP (and Protein Factory) had it for like $4-5.00 per pound for many years, so it was a no brainer back then.
Milk Protein Isolate and Pea protein...everything else mostly is more expensive.
Anyway....