It somewhat depends what you are going to do with these LEDs. You get what you pay for to some degree. f you are using these LEDs side by side and want them to have comparable light output then things get more expensive.
The LED manufacturing process is not a discrete process and produces LEDs within a relatively wide range of light outputs. The range is so to speak sliced into sections and any LEDs that fall into that section of similar light output go into that bin, which gives that process it's name. Binning. So getting LEDs out of a higher Bin usually yields a higher light output with the same drive current but also at a higher expense.
The cheap stuff on ebay is usually from the lower bins which also cover a greater range of light outputs so these LEDs my have perceivable differences in brightness.
What quantities are you speaking about ?
What do you want to illuminate ? a 350mA LED can illuminate quite a bit. I use 5 700mA LEDs with fading colors in my project trippylighting.com, so they are not all at 100% duty cycle and that provides enough light for my living room.