2003 Nissan Altima White Smoke & timing belt

Hello, my question is: I took my car for a repair estimate. It is throwing out white smoke when we start it in the morning (cold starts only) and makes a rattleing noise as well. I took it in for a assesment & estimatement. We are told that the head gasket seal needs to be replace and the two timing chains need to be worked on. The estimate cost is $+3500. is is too high or accurate ?

Thank You
Pete Pina
trespinas@grandecom.net
ph: 210-223-9063
Cell: 210-478-7650