How to access the input tag value

How to access the value after pay now $ in the tag with id payment-sub-btn in the code below to payModal() function I have finalPrice variable finalPrice = document.getElementById('payment-sub-btn').textContent; I try using by getting element by id but it says NaN probably cause its getting the text as well pay now $ with it is there any way to just get the value which is integer value and no text along with it?

 <div class="modal-body" style="background-color: #F6F9FC">
            {{-- Display a Payment Form --}}
            <form method="post" id="payment-form" class="m-1" data-secret="123">
    
              <div class="card-element-hide form-group col-md-12">
    
                <div id="payment-element" class="w3-block" style="min-width:300px!important">
                  <!-- Mount the Payment Element here -->
                </div>
    
              </div>
    
              <div id="coupon-details" class="col-md-12">
                <label class="stripeFontStyle" for="feCoupon"> Coupon Code </label>
                <input type="text" class="form-control form-control-sm stripeBoxStyle" id="lost_coupon"
                  onChange="checkCoupon()" name="lost_coupon" data-dpmaxz-eid="10">
                <p style="visibility:hidden; margin-left:5px;" id="couponMessage"></p>
              </div>
          </div>
          <div class="modal-footer">
            <button class="btn btn-secondary boxShadow" data-dismiss="modal"><i class="fa-solid fa-circle-xmark"></i>
              Close</button>
             
            <button id="payment-sub-btn" class="btn btn-success float-right" style="background-color:#28a745!important"
              onclick="update_coupon();">Pay Now $</button>
            </form>
          </div>

    <script>
    async function payModal() {
      
      await fetch("{{ route('paymentModal') }}")
      .then(response => response.json())
        .then(response => {
          const form = document.getElementById('payment-form');
          _key_for_ss = response.paymentIntent.client_secret;
          paymentIntentID = response.paymentIntent.id;
          finalPrice = document.getElementById('payment-sub-btn').textContent;
          async function openModal() {
            await createCard();
            $('#pay-modal').modal('show');
          }
          openModal();
        })
    }

     var counts = 1;
     var checkboxes;
     var finalPri;
    function add_to_download_entries(data) {
       checkboxes = document.querySelectorAll('input[name="checkWills"]:checked');
        counts = checkboxes.length;
      if($.inArray(data, selected_lostwill_array) >= 0){
        selected_lostwill_array = $.grep(selected_lostwill_array, function(value){
             return value != data;
           });
         }else{
          selected_lostwill_array.push(data);
         }
         // DataTables Functions 
    $(document).ready( function () {
        $('#org_lost_table').DataTable();
        $('#all_lost_table').DataTable();
        if(counts>0){
             finalPri = "Pay Now $" + Number(counts) * Number(22);
            
            $( "#payment-sub-btn" ).text(finalPri);
           }else $( "#payment-sub-btn" ).text(0); 
    } );
    }
    </script>