I think you have summed it up pretty well, wholesale won't cut it on ebay,and even if it did you would have to buy in serious volume to have a chance of competing against the big sellers.
Liquidation can be a good option, but educate yourself about what to buy, and where to buy it from, because there are pit falls.
Buying liquidated products is like wholesale, the bigger the volume you buy, the bigger your savings, however small carton lots can get you started in this business.
Both jimmy and myself deal in liquidated stock so feel free to ask either one of us for any specific advice.
Second hand items won't give you the same reliable source, but you can find some great stuff that will also give you great margin, and can do very well on sites such as ebay, and of course $50.00 can buy you a lot when going to yard sales and weekend markets.
You have to be a smart shopper and be prepared to haggle for the best price, but second hand is a good avenue to look at.
As for selling avenues, ebay will give you the most traffic, and therefore a better selling opportunity. Bonanzle is great because it does provide you a free platform to work from, and everyone there is trying hard to increase traffic to the site overall, but at the moment I would doubt if your would have strong sales potential there.
Stay away from your own developing your own site, not worth the drama, especially when a site like bonanzle offers you pretty much everything you really to start trading, and costs you nothing, not even hosting, if you aren't making sales.
We use a booth at bonanzle to sell out liquidated stock, it's great for us, but we drive traffic there from other avenues, and our market is also different, as we are a b2b structure.
In summary, ebay will give you the best selling avenue, second hand and liquidated stock sources can provide you with a buying avenue.