One way to help decide if an E-bay light is any good, ask the seller what brand LED's are used, then ask for the bin number details. If they can't tell you what bin number the LED's are then I wouldn't bother with them. If you do get the bin number, say they are Cree, check that against the Cree bin chart. That will give you the specs on the LED output.
You can get a cool white 3w Cree off any " Chinese bulk buy" website for $0.75, or a cool white 3w Cree off any of the known DIY sites for $5.00. The difference is what bin number they come from. I wouldn't even bother with a $0.50 LED.