Rebekah
Unfortunately, you are faced with a number of problems. Firstly, the concept. If someone really did know the "secrets to making money on eBay", why on earth would they tell everyone? Their plan is to create thousands of competitors for themselves, thereby driving the prices down - all to sell a $20 eBook. Not a very sound business plan as far as I'm concerned. So, this means that the concept doesn't really work as well as they say, they aren't telling you everything or they just have no idea about business.
So what you are faced with are hundreds or even thousands of people who have exactly the same info as you. Considering I get spammed about eBay secrets at least three times a day, it's probably thousands of competitiors. Also, you aren't getting their secret list of dropshippers - these are all businesses that are available to anyone and, more importantly, they aren't secret as thousands of people now know about them.
You have essentially plunged into business of the offline variety - real products bought from wholesalers. So, just like an offline business, you have a couple of choices - you need to find dropshippers that your competitors don't know about. No idea how to do this unfortunately. There is also an option to just sell products that no-one else has access to such as things from local business - but you need to ship it.
The other option is probably the answer to the problem you are having - pretty much anyone gives a discount when you buy in bulk. You need to somehow judge the market, go to the dropshippers and say how much will they cost if I buy 100?
The last option is don't sell on eBay. There are plenty of other auction sites. Find ones that are popular but aren't flooded with products from people who own the same book that you do.
Sorry if I sound a bit cynical - I hope this helps in some way.
Sean Burns
WebmastersReference.com