What is plastic moulding meaning?
Plastic Moulding, as a manufacturing term, refers to processes that transform plastics into shaped items by putting usually molten, but not always so, plastic into a Mould in order to replicate the interior shape of that Mould. Sometimes the item will be hollow.

It depends of a few different things;
What your project is and what you already have (cad designs etc)
What materials you want to use (what is needed, eg - silicone)
Who your manufacturer is (this will vary the cost)

The injection mould cost has two main components – the mold base and the machining of the cavities.

Injection Mould is the biggest cost of manufacturing a plastic part. Here we share some advices about reducing the cost of mould making.

A good mold maker understand the design of the part and will consider correct shrinkage
Read the plastics material guide to understand the minimum capabilities of the plastic.
A good designer will always plan for even distribution of thickness in the plastic product.

Yes, they are different.

Metal injection molding is process for metal parts.

Plastic injection molding is process for plastic and rubber parts.

Metal injection molding is usually called die casting.

The two processes are similar, injection molded into a mold, and then cool down to get parts.

So many uncertain elements that nobody can give you the exact estimation. The biggest cost driver is the part size. If the part is big, then the mold should also be big, the the mold cost is higher.
1,About the design or samples or prototypes. 2,About the quote elements: 2) mold material 3) Part material