A 15-0-15 transformer will let you build a power supply will give the appropriate rail voltage. You will probably want a VA rating of 100 for two channels of heavy 4-ohm use. Use am enclosed E-I type - at this power level they are common and dirt cheap. You should be able to find these in Digikey or Jameco l.
If you want something discrete rather than an IC amp, look a G,Randy Slone "Audiophiles Project Source Book", page 149. Increase the transformer rating as decribed and add a third parrallel output device. (Or maybe substitute TIP3055/2955). Ibuilt this exactly as decribed and it quite nice. It will blow away the IC-amps without mercy.
I meant cheapest DIY solution, I am planning on putting this inside of a speaker system, so that's my use, so it needs to be efficent, I am making an active monitor, essentially (although it's not a monitor in the fact that it is decidedly low-fi).