In general the most successfull ebay powersellers make on average 1 to 5 dollars for each transaction. You might not think thats alot but if you consider that you should sell more to make more then your on the right track. Most of my auctions I bring in 3-5 dollars profit on each item sold. But if you consider that the number 1 powerseller on ebay averages 18,000 feedbacks recieved each month meaning he sells possibly on average 23,000-28,000 items a month due to repeat buyers.
Multiply 28,000 by 5 dollars. That means he makes $140,000 in profits each month on average. But in actuallity he profits more around 5-9 dollars each item so he makes alot more then I stated.
You can try your luck on high dollar items but you will fare well if you start with the low dollar items that generate small profit.