Well, it would depend on the product. What you need to do is decide what product that you want to sell. After you do that, then do a completed listing search on ebay and see what that item is selling at. Or better yet use a program like hammer tap to get your information.
Once you know what that product is normally selling for, you will then know at what price you have to have. You are looking for a 'cost per item'. After you decide what that 'cost per item' figure must be, then start contacting suppliers and get quotes on what quantities you need to buy in order to get the proper 'cost per item' that will allow you to make a profit and compete with the other sellers....
It just takes a bit of homework, but it's not hard to do...Keep in mind that the larger quantity that you buy the lower your cost per item will be..For instant if you buy 10 dvd's from a supplier, he will probably sell them to you for let's say 5 dollars apeice. But if you bought 100 dvd's he would probably sell them to you for 1 dollar apeice. In other words, you bought a large quantity so you got a lower cost per item on the 100 purchase than you did on the 10 purchase...
Alot of sellers on ebay are not buying from wholesalers as ebay is a BELOW WHOLESALE market.. Alot of the sellers you see selling at such low prices are buying from liquidators, closeout and surplus dealers. They are buying a pallet load or truck load and getting the item for pennies on the dollar...This keep their cost per item very low, and way below wholesale cost...So if you are not looking for a specific product, you should looking into buying a variety of goods through liquidation sales...If you are looking for a particular product, then you need to buy in large volumn to get the low cost per item price...
But there is no magic number such as 50 grand or 500 grand. It will all depend on either the particular product, or the particular variety of products that you are interested in selling...
That being said, liquidations and closeouts are probably the cheapest way to go, as you can buy some truckloads for as low as 7 to 8 grand, which is normally about 24 pallets on an average truck, and the resale value would probably be around 20 grand..And of course it would again depend on what type of goods you purchased.....