[SalesForce] How to calculate the row values in apex:repeat

Your relatedObjectRow class, in addition to having a boolean on it for selected, can have a string value on it for the quantity. Your <apex:inputText /> would then bind to this string value.

Note: I think you've anonymized your objects and these are really sObjects we are talking about, but the same mechanism still applies. The concept is known as using a "wrapper class".

public class relatedObjectRow {
    public string Id            { get; set; }
    public string Name          { get; set; }
    public boolean selected     { get; set; }
    public string EnteredValue  { get; set; }
}

And the VF markup

<apex:pageBlockTable value="{!child.objectRows}" var="objectRow" >

    <apex:column headerValue="Clone" width="10px">
        <apex:inputCheckbox value="{!objectRow.selected}"/>
    </apex:column>
    <apex:column headerValue="PO-Details" width="20px" >
        <a target="_blank" href="/{!objectRow.Id}" style="text-decoration:none">{!objectRow.Name}</a>
    </apex:column>
    <apex:column headerValue="Enter Qty" width="20px">
        <apex:inputText value="{!objectRow.EnteredValue}"  />
    </apex:column> 

</apex:pageBlockTable>

Update: here is a modification that does not use strings, instead using the objects directly.

public void cloneSelectedObjects2(){

    SOStoupload = new List<Purchase_Order_Details__c>();

    for (relatedObjects relatedObject : objectChildren) {
        List<relatedObjectRow> selectedRelatedRows = new List<relatedObjectRow>();

        for (relatedObjectRow row : relatedObject.objectRows) {
            if (row.selected) {
                selectedRelatedRows.add(row);
            } 
        }

        //here for loop to get values
        for (relatedObjectRow row : selectedRelatedRows) {

            //create new pODetails
            Purchase_Order_Details__c pod = new Purchase_Order_Details__c();

            // not sure where this objecttext is coming from
            pod.Purchase_Order__c = objecttext;

            // use the sObject.get() to grab the ID field value from the inner object
            pod.NRProducts__c = row.obj.get('Id');

            // get the 'entered value' from the wrapper class and convert to decimal
            pod.Qty_NR__c = Decimal.valueOf(row.EnteredValue);


            SOStoupload.add(pod);

        }
    }

    insert SOStoupload;  

}

The DOM Id values in Visualforce tables include a row number (the :0: in your JavaScript) so your logic needs to incorporate that. The approach that I think works best is to use a CSS class (that has no markup associated with it) instead of the DOM Id:

<apex:column headerValue="Delivered Quantity" >
    <apex:inputtext value="{!dw.quantity}" styleClass="quantityMarker"/>
</apex:column>
<apex:column value="{!dw.lineItemObj.Rate__c }" styleClass="rateMarker"/>
<apex:column headerValue="Total">
    <apex:outputtext styleClass="totalMarker"/>
    <apex:facet name="footer">
        <apex:outputtext styleClass="grandTotalMarker"/>
    </apex:facet>
</apex:column>

While you could achieve what you want with just JavaScript, I would recommend adding (as a static resource) and using jQuery in your page. The code then becomes something like this (that you should add to the end of the page so the page rendering is not held up):

<script src="{!$Resource.jQuery}"></script>
<script>
(function($) {
    $(document).ready(function() {
        $('.quantityMarker').change(function() {

            var defaultedFloat = function(s) {
                if (s !== null && s !== '') {
                    var r = parseFloat(s);
                    if (!isNaN(r)) return r;
                }
                return 0;
            };

            // Recalculate the row
            var q = $(this);
            var r = q.closest('tr').find('.rateMarker');
            var t = q.closest('tr').find('.totalMarker');
            // Better handling of rounding may be needed
            t.text(defaultedFloat(q.val()) * defaultedFloat(r.text()));

            // Recalculate total of all rows
            var total = 0;
            $('.totalMarker').each(function() {
                var t = $(this);
                total += defaultedFloat(t.text());
            });
            $('.grandTotalMarker').text(total);
        });
    });
})(jQuery.noConflict());
</script>

This code:

• Executes jQuery.noConflict() so any existing value of $ in the page is preserved
• Waits until the DOM is ready
• Then adds a function that is notified of changes on all elements that have class .quantityMarker
• When a change happens, the function finds the class rateMarker element in the same row and the totalMarker element in the same row
• Then sets the product in the totalMarker element = Then sums all the row totals into the grand total