JSFiddle - React, Tailwind, and code Playground

HTML

<form id="cakeform">
               <h2>Need a venue?</h2>
            <p>Avoid the red tape and book a marquee</p>
            <p>What package would you like to order?</p>
            <select id="marquee_package" name="marquee_package" onchange="calculateMarquee()">
                <option value="Bronze">Bronze</option>
                <option value="Silver">Silver</option>
                <option value="Gold">Gold</option>
            </select>

            <p>How many people will be attending?</p>
            <select id="guests" name="guests" onchange="calculateMarquee()">
                <option value="0">0</option>
                <option value="50">50</option>
                <option value="100">100</option>
                <option value="150">150</option>
                <option value="200">200</option>
                <option value="250">250</option>
            </select>
</form>

JavaScript

function calculateMarquee(){
var theForm = document.forms["cakeform"];

var guests = parseInt(theForm.elements["guests"].value);
var marqueePackage = theForm.elements["marquee_package"].value;
var marqueePrice = 0;

if (marqueePackage === "Bronze"){
    if (guests === 0){
        marqueePrice = 0;
    }
    if (guests === 50){
        marqueePrice = 650;
    }
    if (guests === 100){
        marqueePrice = 950;
    }
    if (guests === 150){
        marqueePrice = 1400;
    }
    if (guests === 200){
        marqueePrice = 1850;
    }
    if (guests === 250){
        marqueePrice = 2400;
    }
} else if (marqueePackage === "Silver"){
    if (guests === 0){
        marqueePrice = 0;
    }
    if (guests === 50){
        marqueePrice = 1100;
    }
    if (guests === 100){
        marqueePrice = 2150;
    }
    if (guests === 150){
        marqueePrice = 2550;
    }
    if (guests === 200){
        marqueePrice = 4100;
    }
    if (guests === 250){
        marqueePrice = 5100;
    }
} else { //gold
    if (guests === 0){
        marqueePrice = 0;
    }
    if (guests === 50){
        marqueePrice = 1900;
    }
    if (guests === 100){
        marqueePrice = 2800;
    }
    if (guests === 150){
        marqueePrice = 3200;
    }
    if (guests === 200){
        marqueePrice = 4750;
    }
    if (guests === 250){
        marqueePrice = 5750;
    }
}
alert(marqueePrice);
}