There are two different priced necropsy prices in most cases, there is a gross and then one that encompasses the gross but includes histopathology. In general it is the histopathology that bumps up the price of the necropsy as it requires taking samples, preparing them and having a veterinary pathologist read them for evidence (and this can be many slides from one animal). A gross necropsy is going to look for macrocauses of death, things like abscesses without a determination of species in the abscess, fatty liver, broken bones etc but a lot of vets send the animal out for a gross necropsy which can significantly increase the cost of the necropsy.
In general the price does not have to be along those lines as PCR can be done at a significantly reduced cost for a wide number of diseases ranging from inclusion body disease (IBD), to Cryptosporidium for about $18 a test (plus shipping of samples) by independent companies. See
http://www.vetdna.com/test-type/reptiles for a list at one company.
Most PCR tests can be run on a cloacal, or oral swab as well as possibly on a fecal (contact the company for details on sampling) so there is a lot less of a reason to not quarantine and determine what is present in a collection before issues happen.
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Ed