The cost of a mould is not really a function of how big the part is. It is a function of how many cavities you asked for, how long the tool has to survive, how many moving pieces the geometry forces into it, and how good the surface has to be. Each of those is a decision rather than a fact, which is why two quotes for one part can be far apart and both honest.
Cavity count is the biggest single lever
Doubling cavities does not double the tool price, but it moves it a long way, and it halves the machine time per part. The right count comes from the annual volume, the cycle time and the machine that will run it. Guessing high is a common and expensive mistake, because unused cavities are capital sitting idle in a shop that is charging you to store the tool.
Steel grade and expected life
An aluminium tool is quick to cut and suits short runs and bridge production. Pre hardened steel is the default for mid volume work. Hardened and coated steel is what abrasive glass filled resin demands if the cavity is to keep its dimensions. Quote the tool against a number of shots, because a tool designed for fifty thousand and a tool designed for a million are different objects.
Actions, lifters and everything that moves
Every undercut needs something to move out of the way before the part can eject: a side action, a lifter, a collapsing core or an unscrewing mechanism. Each one adds design, parts, assembly, maintenance and risk. A designer who removes an undercut by moving a snap feature to the parting line has just taken a large amount out of the tool price.
Finish, texture and the last few percent
A polished optical cavity and a lightly textured one are very different amounts of hand work, and texture is applied to the finished cavity as a separate operation with its own cost. Specify the finish where the part is seen and let the rest be as machined. Also budget for the sampling loop, because almost no tool is right on the first shot.
Questions people ask about injection mould cost
What does an injection mould cost?
It depends almost entirely on cavity count, steel, actions and finish rather than on part size, so a small complex part can easily cost more to tool than a large simple one. Get the quote broken into those elements.
Can I start with a cheap tool?
Yes. A single cavity aluminium tool is a normal way to bridge to production while volume is proven, and the money spent is small compared with a multi cavity steel tool that turns out not to be needed.
Who pays for tool maintenance?
Usually the moulder does routine maintenance and the owner pays for wear items and damage, but this must be written down. Ask for a shot counter reading with each order.
Why did the tool need modifying after the first samples?
Because steel can be removed but not easily added. Toolmakers deliberately leave cavities slightly full so dimensions can be corrected after the first shots, and that adjustment loop is a normal part of the programme.