I buy my whey from either Protein factory or DPSnutrition. It's about the same price depending on what you get.
Think about this for a minute. Whey has lactoferrin, which aids in growth and isolates do not have this. Whey is 80% protein and isolate is close to 90% protein, why would you pay double the price for 10% more protein? And as far as the Dalton mix, which is theoretically faster than whey, whey is in your system in less than 20 min. isn't that fast enough already? And it lasts 2 hours. That's why i opt for 2 shakes, to cover the full 4 hour window.