I frequently have this problem. Yes, they should be made to display the top price at the time of enquiring. I found a flight recently for £5 which then went up to £80 by the time I'd paid for taxes, airport security, luggage, etc. I didn't bother booking it, and found a cheaper one elsewhere.
it has happened to me too dusty, I heard something on the News yesterday, that The Adverising Standards were investigating this practise known as Drip Selling!
not before time too