I will have questions while putting my noze into the php codes and the structure of the database - after that I can really tell you how much work it will require.
Then I may be able to give you a better quotation for the new functionality set-up.
I'll charge the hour at 25$, up to my bid (200$), if it does come less, you will pay less (or get a credit - I am new on this website I am not too sure yet how the payment thing is working), but if more, obviously the difference is for me.
Do not hesitate to inquire about my experience, thanks for reading.
Best regards
Michaël