How do you determine the value of mold(s)?

I am looking at investing in a collection of molds for my business. I currently have a fiberglass boat repair shop but my goal is to move to all boat part production. Parts like these http://cmmarineproducts.com/
The majority of the molds are professionally made and very nice, although it shows that they have been used and passed around. They are mostly on metal frames and casters. It is a lot of about 70 parts. 50 ish high quality molds made by Marine Concepts, and then about 20 molds made by various people in various levels of quality. Some little more than glorified plugs.
How do i determine if it is a good investment, and if the asking price is reasonable?

I plan to also invest in a resin/gecoat/chopper system if I buy the mold set.

Any advice appreciated. Thanks in advance