So go to bookmarks click add bookmark and then for the url part paste this:
javascript:{var tI=document.body.innerHTML.match(/oldcost_/g).length; var worth =0; for (var ji=1; ji<=tI; ji++){worth+=parseInt(document.getElementsByTagName('form')[2].getElementsByTagName('table')[0].getElementsByTagName('td')[9+((ji-1)*7)].innerHTML.replace('<b>','').replace('</b>',''))*parseInt(document.getElementsByName('cost_'+ji)[0].value);}alert('Page Worth: '+worth+' NP');}
Call it whatever. I call it "NeoPets Bookmarklet - Shop Inventory Page Worth"
I find it useful. You might