just like to put my 2 cents in here...
i am an ebay seller for car audio and the difference between such places like
crutchfield and
ebay is basically the warranty. any online sales void the manufacturer warranty which is why you can get the stuff for half the retail price.
crutchfield will charge more because they are one of the few authorized online dealers. if your willing to take a chance without a warranty then
ebay is the best way to go, especially if you plan on abusing the items since that just voids the warranty.
ebay prices are pretty much wholesale prices that dealers like me get them from distributors. we only make a few dollars profit for each item sold when we buy bulk. go ahead and ask any
ebay seller if you can see a picture of the serial number on items and they wont because they are scratched off and defaced, only reason being is because the manufacturer won't warrant the item.
another thing with ebay sellers is they also like to cheat you to make money. anything that they sell and they offer you a 90 day warranty means its refurbished and just stating its brand new because you really can't tell. they also like to sell open box items and stating brand new because they make money that way. if your looking to get anything from
ebay spend a few extra dollars and buy from someone who will honor a 1 year warranty through them.