I just recently bought a used projector (Hitachi ED-A100). The only reason I bought it is so I can watch the worldchampionship soccer on a big screen with my friends. According to the projector itself, the lamp only has 150 hours on it but I realize that number can be tampered with. So to make sure I'm prepared when the bulb goes, I want to buy a spare one. Problem is, through the "official" channels (projector shops), the bulb is close to $300. But when I look on eBay, I see them for $70. Also, I see they are mostly being sold including the bulb housing, but also just the bulb alone. So what's the difference between the "cheap" eBay bulbs and the bulbs I can buy at the store? And why would I need to buy the bulb with housing? Thanks in advance.