Assuming your are registering courses as \"events\", then there is no way to do this currently as you can only register for one event at a time. However, if the different courses are setup as custom field options where the user selects the courses they want and are charged a fee for each one they select (custom fee fields), I would suggest adding this...
Add a custom field like \"How many courses are you signing up for?\" Make it a dropdown selection field and check the \"fee field\" box. For the field options, enter:
1|2|3
For the field option fees, enter:
0|0|-51
what this will do is take $51 off of the total price if they say they are registering for 3 courses.