So yours is a 2004? I didn't think the diamond key was still available for a car nearing 20 years old. But for $120, that actually seems rather reasonable. I bought a blank FOB on ebay for $20 and then cutting it would take like $40-50...almost worth to get the right thing.

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2003 BMW X5 3.0i -- MT5, 3.64s final gears, H&R lowering springs, K-Mac bushing kit
2007 BMW X3 3.0Si -- MT6