* AMP allows A$290 mln for bad monetary advice
* business spending another A$150 mln investigating practices
* Shares at their cheapest since 2003 (Adds analyst comment, updates shares)
By Byron Kaye and Paulina Duran
SYDNEY, July 27 (Reuters) – Australia’s biggest wide range supervisor, AMP Ltd, on Friday flagged A$530 million ($391.4 million) of costs stemming from an inquiry into economic sector misconduct and warned first-half revenue would decrease, delivering its stocks up to a 15-year low. Continue reading IMPROVE 3-Australia’s AMP matters the expense of previous misdeeds, stocks plunge