I buy all of my bras at Victoria's Secret. They have customized fitters there, who know how to size properly and their prices are lower than Nordstrom. Victoria's Secret bras go for $50 or so (unless they're 100% cotton, those are cheaper - but they aren't as supportive imo) and it's well-worth the price! If you know your size for sure, I'd recommend checking them out online. They carry a larger range of sizes and styles online than they do in the store. Shipment is very fast and reasonable too.

Best wishes!