Just a little curious. Why do you want to buy course materials from ebay? Is it that much cheaper than your ldc ?
My only reservation would be that you get the right stuff. There are several different crew paks available (IE;cd rom version, book + video, book only, book video recreational dive planner) There are also 2 versions of the RDP, be sure you know which your instructor intends to use in the course (of course knowing how to use them both is beneficial).
Most dive centers add all of the nessessary paperwork for the course (ie: student training record, log book, PIC card, etc).
The PIC cards are not included in the crew pak. You could find that later you need to pay the extra $14 for a pic card.
Personally I would support the ldc who is teaching me, unless they were really goudging me.
I guess it's kinda like buying brake pads from ebay just to save$8), then bringing them to your local mechanic, and asking him/her to intall them.
My mechanic has a sign on the wall that reads "Labor rates, with our parts $25 p/hr, with your parts $35 p/hr. Or course it's just a joke, but I can appreciate it.
I worked at a dive center that offered the OW class for $345 which included EVERYTHING, from class materials to rental gear. However that was a discounted package for people who bought their , m/s &fins there. A la Carte, the class was $395. The result, you have to save over $50 in order to make it worth it.
Might be a good idea to discuss this with your instructor.