select value to another value show with javascript || selected value according price and rate show with javascript

selected value according price and rate show with javascript, Set and get range values, text, or formulas using the Excel JavaScript API

<html><head></head><body> <form action="" method="POST">
<div style="width:100%; margin-left:1%;">
<div class="col-sm-3">
<btn-primary6 class="m-0 font-weight-bold text-primary">Update Account Mode
<select name="accountmode" onchange="myaccountmode(this.value)"  class="form-control">
    <option> <?php echo $row['accountmode'];?> </option>
<option> Select Account Mode </option>
<option value="Paid Plan"> Paid Plan 50% off</option>
<option value="Plus Plan"> Plus Plan 80% off</option>
</select>
</btn-primary6></div>
<div class="col-sm-3">
<btn-primary6 class="m-0 font-weight-bold text-primary">Selected Plan Price 
<input required="required" type="text" class="form-control" placeholder="auto show plan price"  name="planprice" id="charges" >
</btn-primary6></div>
<div class="col-sm-3">
<btn-primary6 class="m-0 font-weight-bold text-primary">Upgrade Users 
<button class="btn btn-primary bg-danger text-white btn-block" name="Upgrade" type="submit">Upgrade</button>
</btn-primary6></div>
</div>
</form>
<script>
function myUSER(value) {
  document.getElementById("username").value = "" + value;
}			  
</script>
<script>
function myaccountmode(value) {

 if(value=="Paid Plan"){
	document.getElementById("charges").value = "Upgrade Charges Rs.<?php echo 99;?>";	
	}else if(value=="Plus Plan"){
    document.getElementById("charges").value = "Upgrade Charges Rs.<?php echo 199;?>";
	}else{
	document.getElementById("charges").value = "Upgrade Charges Rs.0";	
	}
}			  
</script>
   

</body></html>
HTML

Output:-

 

Another:-

The best way to achieve this is to use javascript.

<select id="dropdown">
  <option value="1.00">$1.00</option>
  <option value="12.43">$12.43</option>
  <option value="37.21">$37.21</option>
</select>

JavaScript:

var e = document.getElementById("dropdown");
var value = e.options[e.selectedIndex].value; // The value
var text = e.options[e.selectedIndex].text; // The text

Or jQuery:

$("#dropdown :selected").text(); // The text
$("#dropdown").val(); // The value