For calculating magic items that don’t take up slots:<br/><br/><div class="quoteheader"><div class="topslice_quote">Quote</div></div><blockquote class="bbc_standard_quote">Calculate the price of the single most costly ability, then add 75% of the value of the next most costly ability, plus one-half the value of any other abilities.</blockquote><div class="quotefooter"><div class="botslice_quote"></div></div><br/>Keep in mind that taking a slotted ability and making it slotless doubles its cost.  As for combining multiple slotted magic items:<br/><br/><div class="quoteheader"><div class="topslice_quote">Quote</div></div><blockquote class="bbc_standard_quote">Calculate the price of the most costly ability, then add 1.5x the value of any other added abilities</blockquote><div class="quotefooter"><div class="botslice_quote"></div></div><br/>Edit: And of course the Magic Item Compendium has a list of common magic item effects (ability enhancers, save boosters and such) that can be added on to certain magic item slots without increasing the price.