Think of it like this. A perfect weapon upgrade can go up to about 60k. Your's is one off perfect. And since perfect;s really jack up the price, you should try and sell it for around 40k. Tell people it is very rare and only one off perfect. Make sure the customer know's perfect is worth about 60k, and say something like: "This is only ONE HP off perfect, and I am knocking 20k off of it because of that, if you ask me, that is a screaming deal."
Note, that you will have to be patient, you will have to wait for the right customer, so just take your time and make sure you dont sell it cheap to someone just to get rid of it. If you are really desperate, go no lower than 30-35k.
Good lucks
And remeber, BE PATIENT