How to get value from Javascript to input text form?

I have a select form with kinds of hotel rooms like ordinary, family, deluxe, executive and so on each of it has a corresponding price let us say in ordinary room i will set $300 price.

At the right side of the select form everytime I choose let us say ordinary room the right side input text field it will reveal the price $300. So basically I use java script with the code var ordinary=document.getElementByID("ord").value so that i can set the price so, var ordinary= 3500. The next is getting the value from variable ordinary to be reveal in input text field every time I choose the Ordinary room in the selection form, but how am i going to do that?

Here's the code

<script language="javascript" type="text/javascript">
    var ordinary= document.getElementById("ord").value;
    var ordinary= 5300;

</script>

<form action="insert.php" method="post">
    <table align="center"><tr><td>
            <font face="Arial, Helvetica, sans-serif">RESERVATIONS</font> 
        </td></tr><hr color="#00CC99"/> <br/>
    </table>
    <table border="0" align="center">
        <tr>    
            <th align="justify"> Name: &nbsp </th> 
            <td><input type="text" name="name"></td> 
        </tr>
        <tr>
            <th align="justify"> Contact Number: &nbsp; </th> 
            <td><input type="text" name="contact"></td> 
        </tr>
        <tr>
            <th  align="justify">Room Type: &nbsp;</th>
        <td>
            <select name="roomType">
                <option value="---">---------------------------</option>
                <option value="Ordinary " id="ord">Ordinary</option>
                <option value="Family ">Family</option>
                <option value="Superior ">Superior</option>
                <option value="Deluxe ">Deluxe</option>
                <option value="Corner Suite King">Corner Suite King</option>
                <option value="Executive ">Executive</option>
                <option value="Executive Suite">Executive Suite</option>
                <option value="Grand Executive">Grand Executive</option>
                <option value="Presidential ">Presidential</option>
            </select>
        </td>
            <td>

            </td>
        </tr>
        <tr>
            <th align="justify">AddOn Services: &nbsp;</th>
        </tr>
    </table>
</form>

Solution

Give the select an id of roomType and then use this

var e = document.getElementById("roomType");
var desiredValue = e.options[e.selectedIndex].value;

The value for options should be the desired data for your script. You should call the selectedIndex of the select element rather than the options, otherwise that would be a lot of code we would all have to type...no fun

    <select name="roomType" id="roomType">
        <option value="---">---------------------------</option>
        <option value="5300">Ordinary</option>
        <option value="SomePrice">Family</option>
        <option value="SomePrice">Superior</option>
        <option value="SomePrice">Deluxe</option>
        <option value="SomePrice">Corner Suite King</option>
        <option value="SomePrice">Executive</option>
        <option value="SomePrice">Executive Suite</option>
        <option value="SomePrice">Grand Executive</option>
        <option value="SomePrice">Presidential</option>
    </select>

Change SomePrice to your desired values.