Last I heard a 40 watt equivalent LED array sold for about $39 USA and came equipped with the power supply built into the base, which can be screw into any lamp designed for a standard incandescent bulb. You can also buy individual LEDs with wire leads to build your own array. Most need 3 volts or a bit more, so you can light one or more in parallel with 2 each alkaline batteries, or 4 in series with a 12 volt battery. To light 57 LEDs in series with 120 volts ac or 100 LED with 220 volts ac, they can be connected in series with a1/10th amp fuse and a diode, which produces dc pulses, which improves efficiency over dc. This does not however provide protection from power line surges, so you should likely obtain a supply designed for LEDs. These were sold with about 35 LEDs in series by General Electric Corp. for about $8 USA, the last two Decembers for Christmas lighting. The power supply is a green lump in the wiring about one inch long, which possibly contains a SCR = silicon control rectifier and an Integrated circuit to optimize the current flow and protect from line surges. I have one sting in my house that has operated continuously for almost 15 months, and still going except for two of the 35 LEDs. Outside, in the rain, they typically fail after about 4000 hours of operation. The 35 LEDs are equivalent to about one 15 watt incandescent = not very much light. The ones I bought 3 months ago are a bit brighter, so the technology is improving.
If you decide to build the 57 or 100 LED with a diode supply you can likely remove a few of the LEDs so the remaining ones are brighter. Caution: if you remove one too many you may destroy all of them Neil