You can detail all of your operating & material( including development and maintain a website )cost down to the penny. That said, the market will only pay so much for a product. You have to establish & separate yourself from the mega injection companies w/ superior ,quality products. This requires years and more $ then you'd ever expect to spend. A small,well organized hand injection business is most difficult to fully support the cost of a basic lifestyle.Distance yourself from the gimme,gimme crowd and consignment stores and you'll have some extra income @ the end of the year. Self-satisfaction from creating your own ,successful product w/ an expanding,repeat customer base is paramount to your success.
The cost of multiple cavity injection molds are expensive but they work & produce for a lifetime as plastisol cost keep re-occurring month after month after year