There are many manufactures making e-Ballast.IceCap
Coralife
etc.
Generally, the PC ballast is cheaper then the VHO ballast. The PC bulbs is a little more expensive then the VHO bulbs.
You will get more light from 2x110 VHO than the 2x55 PC. I have never compare 4x55 PC with 2x110 VHO. If we look at the wattage they are the same, but ppl claimed there is more light from the PC. Which I do not believed.
the 4x55 PC will definitely cost more then the 2x110 VHO.
Let's run some number:
Power Compact
from AH supply
2 x 55 watt Bright Kit™ $64.99 x 2 kit = $130
55 W PC bulb: $22 x 4 bulbs = $88 (AH supply)
Cost about $210
from HelloLights
4x55 PC retrofit $225 (on sale) including bubls)
VHO
from HelloLights
2x110 VHO retro kits $155
2x110 VHO bulbs $22 x 2 = $44
Cost about $199
from other source
2x110 VHO ballast about $50
2x110 bulbs $44
reflector 48" about $30
Cost about $124