The thank you page ([url removed, login to view]) will need to echo the order total. If a client orders a server for $19.99 it will need to spit out 19.99
If you can't complete this project on time and with good communication don't make a bid. I've already been burned by a bad freelancer once already.
This needs to be done without access to our production WHMCS system/files. I can provide the [url removed, login to view] though.