I definitely agree that this is not a big ethical breach in terms of magnitude, but it is still better not to look. Apparently this is not intended to be public information. If this information is private, I guess the companies want to derive some (slight) competitive advantage from not sharing it. I think you could make a strong argument that companies should make their healthcare offerings public knowledge, but they aren't currently (I guess?). In any case, access should be granted on the basis of an even playing field.

>What harm was done by someone comparing prices?

It removes the information asymmetry, which protect the profits of the seller.

Exactly. So, no harm to any real people.

If you accessed my medical records, nobody would be “harmed” as they are fairly normal. It would still be wrong.

Because it would be a privacy issue. But that assumes they're looking at your information on purpose, and not just some price tags.