Correct me if I am wrong. In this case, the processing fee consists the following :
1) The $75 for the sponsor
2) $75 for the principal applicant (OP) who is a under 22 years of age and not married or in a common-law or conjugal relationship
And the above have to be paid before the application is submitted, and proof sent with the application. The $490 RPRF can be deferred until later in the process - you can pay it at any time, or wait for them to request it, but they won't issue the visa until it's been received.