JSFiddle - React, Tailwind, and code Playground

HTML

<table class="productTable productSmall" cellspacing="0">
    <tbody>
        <tr>
            <td style="width: 27%;">
               <strong>American (wild) plum</strong>
            </td>
            <td class="custom-tag"></td>
            <td class="custom-tag">
                Prunus americana
            </td>
            <td class="custom-tag">
                Bare Root
            </td>
            <td class="custom-tag" style="border-right: 2px solid #000;">
                2' - 3' size
            </td>
            <td style="text-align:right;padding-right: 10px;">
                $<span class="priceAmount">1.75</span>
            </td>
            <td class="quantity">
                <input id="Units_4996263" class="productTextInput" name="AddToCart_Amount" value="1" type="text">
            </td>
            <td>
                <input class="subTotal" name="subTotal" readonly="readonly" type="text">
            </td>
       </tr>
   </tbody>
</table>

JavaScript

$(".productTextInput").change(function() {
        var priceAmount = parseFloat($(this).closest("tr").find(".priceAmount").text());
        $(this).closest("tr").find(".subTotal").val(parseInt($(this).val()) * priceAmount)  
    
    });