Content Management Custom Integration with Application

We are looking  at purchasing a software package  and one of the things it lacks is integration  with Content Manager 

The have offered to put together a custom interface  which would allow their application to integrate with Content Manager for the low low price of $4500 

My gut instinct tells me that quote is higher than a cat's back, but in reality I have nothing to really compare it with. When it comes to applications integrating with Content Manager  is there a price range I should be looking at  or any recommendations of 3rd party outfits  that do this type of integrations? 

Any advise would be greatly appreciated 

CM 9.3