Help diverter valve 86 k20

The dealership wants $500.00 for this part good lord where can i get a reasonable price new or used throw me a bone please
86 k20 3/4 ton 4x4 5.7l vin M

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Added this to help if the name confuses
The valve is located just above the air pump and is often refered to as an (anti-backfire valve), it redirects exaust to the cylinders as required .... as to the $$ the dealer wants I was shocked to say the least..... I am lookin for a used one now but I could very well end up with the same problem with a used valve :( at wrote:

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at wrote:

    You might try a Non-autozone type parts store such as a NAPA, or another one that supplies profession mechanics for the majority of their income. Any real Parts Store can take the GM part number and cross referance it to their own brand (such as NAPA) or aftermarket brands.
Charles Bendig
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