Is whey isolate worth the extra money over concentrate?

Sometimes, but less often than the price gap suggests. Isolate is filtered to 90%+ protein with most of the lactose and fat removed; concentrate sits around 70–80% and costs less per gram. If you are lactose-sensitive or chasing the leanest possible macros, isolate earns its premium. For most people the practical difference is small, and the dollars-per-20g-protein number settles it — a well-priced concentrate frequently beats a marked-up isolate on everything but the lactose line. We compute that figure for both so the filtering premium is visible instead of assumed.