Going to the Blue Lagoon is one of the top things to do in Iceland, it's so amazing, beautiful, good for your skin and incredibly expensive, if your not Icelandic.
The listed price on the English site is 28 euros , about 4300 Isk, while on the Icelandic Blue Lagoon home page you see an advertisement for 1500 Isk. This offer is only valid if you are paying with an Icelandic card. If you click on this ad, then try to change the language to English you will only be redirected back to the original Blue Lagoon page (in English), where there is no 1500 Isk offer to be seen.
I have been to the Blue Lagoon several times and have never paid anything near to these crazy prices. Once I was even let in for free because I was with some a walking group, that only advertised in Icelandic, although someone did come and ask what we (I was with a friend) were doing here.
So, clearly, the Blue Lagoon makes all the money off people who can not speak Icelandic.
LESSON OF THE DAY:
Before you come to Iceland, befriend an Icelander. It'll pay off.