Premium is mostly restraint: fewer colours, more space, and copy that sounds sure of itself.
Brands that look expensive make decisions and stick to them. One typeface family, a tight palette, consistent spacing and photography with a clear point of view do more than any effect.
Tone matters as much as design. Short sentences, concrete claims and no shouting. If the product is good, the page does not need to prove it with exclamation marks.
Price signals follow the same rule. Show it calmly, explain the value once, and let the details do the persuading.