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If you go on to the CDC website and look up attic rodent infestations they recommend removing soiled insulation. There are products available such as Steri-Fab which are used to sanitize the attic and will take care of urine etc. The product can be sprayed or applied by a fogging machine which would kill any bacteria which may be present. This would stop you from having to replace all the insulation and is a much cheaper option.
I would remove all heavily soiled insulation, vacuum up any additional xxxx with a Hepa filter vacuum and then sterilize everything with Steri-Fab. You could probably have the sterilization part done for around $500.