A gas tank would more-likely be extrusion blow molded vs injection molded.
Extrusion blow molds are relatively inexpensive (compared to injection tooling). It still costs a few thousand dollars to have a single cavity aluminum production mold built. Prototype molds (which are short-lived and can only produce a limited number of parts) cost less and would probably be the way to go for something as low-volume as this would be.
But that's only half of the task. You will then still need to find a company to run the mold for you unless you happen to have a blow molding machine in your garage. When I have my parts molded there is a minimum quantity because anything less it isn't worth them even installing it in a machine. Subsequently, I don't run my molds but once ever few years or so and then it's usually only for a day and I have another ten years worth of parts.
I make some plastic backglass trim with profile extrusion dies and when I have it run, the minimum order is one-hour run time. Well in one hour the extrusion line can crank out 4 pallets worth of trim already cut to length. I haven't run them in several years now either but still own the tooling.
When I consider a project like this I need to ask myself some questions:
- What is the demand? (How many do I think I can sell?)
- What is the tooling investment cost?
- What are the production costs?
- What's the minimum quantity for production?
- What to set the piece price at?
- How many do I need to sell to break even?
Normally, I go with a 500 piece threshold which means if I don't think I can sell 500 pieces I will usually pass on the project.
If I think I can sell 500 pieces, then I divide my tooling costs by 500 to calculate a piece price. If it looks good, I go with it. I don't start making any profit until after the 1st 500 sold. All of my pinball parts are well past that milestone now and are profitable.
I don't know how many gas tanks you think you can sell but I would double-check the material they are molded from. ABS doesn't have the greatest chemical resistance to gasoline and wouldn't normally be used for a gas tank. Most motorcycle tanks are blow molded from high density polyethelene. Some newer ones are multi-layer plastic for improved barrier properties.
There is another option if you don't think you can sell 500 pieces.
You can have it quoted in Communist China.
Cost is dirt cheap but as you can imagine there are other risks involved in dealing with a company half way around the world that may or may not deliver a quality product to your specifications. Unless you are a big company, you probably aren't going to be making the trip to China to solve any manufacturing or communication issues.
