Should a shampoo normaly be expected to be expensive?
This is probably in relation with the product range of this company which must sell only luxury expensive products. What I propose to you starts from this idea.

So I would translate as above with the following explanations:

unique = unique. I prefer rare which sends the same commercial idea but is far less common. A french idiom says "Tout ce qui est rare est cher". So it should raise some interest in a French brain to put "rare" together with something which means affordable.

Affordable = abordable, bon marché, à la portée de toutes les bourses. I prefer the last expression because it reinforces the contrast and is less common.

However this up to you...

I hope it helps you
Yacine

The above is the correct spelling.
I'm very sorry, I've spelled two words wrongly (by speed of the habit in writing in English)