"A small and simple single cavity plastic injection mold usually costs between $1,000 and $5,000. Very large or complex molds may cost as much as $80,000 or more. On average, a typical mold that produces a relatively simple part small enough to hold in your hand costs around $12,000."
Source:
https://rexplastics.com/plastic-injection-molds/how-much-do-plastic-injection-molds-cost - turned it up on a google search
Getting a new denomination from Matsui requires making a new
component for a
modular mold system. It's not a complete mold, but it is a part of a very complex mold. $3,500 seems like a bargain.