I believe in order to solve this problem you are going to need a more thorough and comprehensive understanding of how your code works. This form is pretty elaborate -- and not especially readable as code goes. It's not clear at all to me which variable is ultimately dictating what the price is. Is it $fee or is it this var in booking.process.php?
$price_per_spot = getPricePerSpot($serviceID);
If I'm not mistaken, it's that second PHP script that actually creates the order and charges people money. Perhaps $fee is just for display purposes?
Your if statement you've concocted above doesn't look quite right. I doubt $date is going to be the string "THURSDAY" and they way you've written it, you are not actually trying to check if $date is equal to "THURSDAY" but rather if it's equal to some constant you've defined called THURSDAY. Constants are defined like this:
define('THURSDAY', 'some-value here');
Since $date appears to be submitted by a user posting a form, I have no idea what format it might be. It looks like your code is relying on [man]strtotime[/man] to turn this string submitted by a user into a UNIX timestamp (read the docs). In that case, it's going to be some integer and will never equal the string "THURSDAY" and probably won't ever equal any value you may define as a constant.
You might want to try looking at the [man]date[/man] function which can take a UNIX timestamp and interpret the time reflected by it as a more human friendly concept such as the day of the week:
$user_submitted_date = "August 3, 2015";
$unix_timestamp = strtotime($user_submitted_date);
echo $unix_timestamp . "\n"; // this will output 1438585200
$day_of_week = date("l", $unix_timestamp); // Monday
It's also sort of hard to tell what's going on because the scripts you've posted refer to functions that simply are not defined in here. Rather than post all that code and expect someone to wade through it all, I would suggest you try and better understand how the system currently stores these prices. I'd suggest using some kind of data structure to determine prices rather than an if statement. You can probably be sure that they'll eventually want some more elaborate pricing scheme and it's harder to maintain thickets of if statements than it is to change some data structure.
