We have no measure by which to judge the cost of building an Iron Man (http://www.imdb.com/title/tt0371746/) suit, as the materials used do not exist in reality.
If “brains-under-the-seat” means its worth seeing, then yes. Even my mother liked it, and she usually hates action movies. I think it appeals to a large audience because it is,of course, an action movie, and it has romantic elements too.
“Brains etc” means that we would see it in the summertime if it were playing nearby and took no effort on our part – like plowing the driveway and putting on the face mask.
This should help if you’re still wondering. Also, in Iron Man 2 a similar suit (the Hammer version) is said to be $125.7 million if I remember correctly.