I repaired my front cv axle boot for around $20 in parts! i suspect he gave you a quote to replace the front axles AND the Diff!!!!
I would question him on that quote! alot of the stuff seems like things you could do yourself with a reasonable level of mechanical ability (and you tube! or this forum!!)

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2003 X5 3.0i (02/2003) sport package, Sapphire black metallic / Black Dakota Sport seats. compass mirror retrofit, trailer hitch retrofit, Prodigy P2 trailer brake controller installed, PDC retrofit, Lumbar support retrofit. heated rear seats retrofitted. Running boards retrofitted and subwoofer install in progress. 4.8is Brakes installed front and back. Bluetooth TCU installed, Rear Fog lights installed. Retrofitted reclining rear seat backs.