<apex:outputField value="{!item.Cost__c}" styleClass="item-cost"/>

<span class="item-cost">
<apex:outputField value="{!item.cost__c}"/>
</span>

<apex:outputPanel layout="block">
<apex:outputField value="{!item.cost__c}"/>
</apex:outputPanel>

<apex:outputField>
   <span class="item-cost">{!item.cost__c}"</span>
</apex:outputField>

<apex:outputField value="{!item.Cost__c}" styleClass="item-cost" />

<apex:pageBlockSectionItem dataStyleClass="item-cost">
    <apex:outputField value="{!item.Cost__c}" />
</apex:pageBlockSectionItem>