Make sure the ballast you get matches the bulb you use. Such as S51 ballast must be used with S51 compatible bulb. You can get a really awesome deal on a 400w metal halide/hps combo set single socket from htgsupply.com for around $170.00 not to advertise but that's a good deal!
SAP420 Reviewed by SAP420 on . Going cheap on an HPS setup? I want to get a 100W HPS setup going, and it looks like I have two options. Here's a ballast for $18, and a bulb for $6: 100 Watt High Pressure Sodium 100 watt HID High Pressure Sodium Bulbs: 1000Bulbs.com And here's a ballast for $50 and a bulb for $17: 100W HPS Ballast Kit S54 Quad Tap - ProLighting.com LU100/MED|C100S54/M|100W HPS Bulb Medium Base Clear - ProLighting.com Rating: 5