I was wondering about this myself and did a little research. typical whey isolate amino acid profile:

Leucine = 11.8g/100g of protein
Isoleucine = 7.3g/100g of protein
Valine = 6.5g/100g of protein

I take two servings of whey isolate per day each containing 45g of protein, this translates to:

Leucine = 10.6g per day
Isoleucine = 6.6g per day
Valine = 5.8g per day

So if one were to purchase a typical 2:1:1 BCAA product and consume 20g per day they would be consuming:

Leucine = 10g per day
Isoleucine = 5g per day
Valine = 5g per day

So you're essentially getting the exact same thing from your whey protein isolate. Some whey isolates may contain more or less BCAA's but that is the typical profile.

I can't justify spending $25/lb on BCAA's when I'm already gettin them in my $8/lb whey isolate.