Small LEDs can be cheap 10 cents each:
Lets look at a LED data sheet: (just picked one from eBay Item: 230274324488)
http://catalog.osram-os.com/jsp/download.jsp?name=LW_A673_Pb_free.pdf&url=media/_en/Graphics/0 0042257_0.pdf

See page 8 Relative luminous intensity vs current.
Yep as the current goes up, the efficiency drops.
If You Need 100ma of brightness, using 10ma ea requires maybe 7 LEDs. For the cost in efficiency I would drive it at 100ma to get the light I need. If the power was the killer then using many LEDs would be better. IF you want lots of light, the 1 watt LED are costly, would not drive then with less current than they are rated for. My thoughts!