Javascript change property of PHP variable according to date in list menu selection

Question

I'm creating a booking form which selects prices and dates from a Mysql databse according to the code transported in the URL.
I have successfully got the form to display dates for this year and next year in a drop down menu/list form item.
However, I would like to change the price according to what year the selected date falls in.
The key variable that needs to change is this $coursefee
If a date in 2009 date (e.g. 2009-10-12) is selected the varibiable $coursefee would change to be
<?php $coursefee=$row_rs_course['price09'];?>
And if a date like 2010-10-12 is selected the varibiable $coursefee would change to be
<?php $coursefee=$row_rs_course['price10'];?>
To complicate matters the menu is dyamically populated too:
<select name="dates" class="course" id="dates">
<?php
do { 
?>
<?php
$date1 = strftime("%d %b",strtotime($row_rs_dates['start_date']));                       
$date2 = strftime("%d %b %Y",strtotime($row_rs_dates['finish-date']));
?>
<option value="<?php echo($date1." - ".$date2); ?>"><?php echo($date1." - ".$date2);?></option>
} while ($row_rs_dates = mysql_fetch_assoc($rs_dates));
  $rows = mysql_num_rows($rs_dates);
if($rows > 0) {
mysql_data_seek($rs_dates, 0);
$row_rs_dates = mysql_fetch_assoc($rs_dates);
</select>
I'm pretty sure the answer lies in the murky world of javascript but unfortunately I haven't the first clue about javascript.
Can anyone help me with this?
Cheers
Dave

Answer 1

Thanks David,
I can see that would work and I'd have no problems doing that but wouldn't that mean that all the oher data the user had fillled in would dissapear?
There are too many fields I think to transfer everything in the URL and the date selection field is way down the form and I think it would seem pretty odd to have it before name address etc. That's why I thought a javascript solution would be more suitable as it needn't rely on a page refresh.
Cheers
Dave