Been doing some research lately on the internet and I've realized that one can easily jump right into the garage kit business without any sculpting skills. Where you can make your own model kits for sale or personal use using the currently available technologies and services. Definitely you'd need drawing, spatial relation skills as well as a fertile imagination. How is this possible? Well by means of outsourced 3D printing services available right now and a little design skill on your part (well you can outsource that too if you like)
The core components you will need are a 3D modeling software that will allow you to design your model kit then the 3D printing service that will charge you for printing your design out in solid form.
For the software to design your model kit you can use the free and open source Blender that is a robust 3D modeling and animation software. There are other commercial grade and paid 3D softwares out there but I'm assuming that we want to keep costs at a minimum that's why I'm sticking to the open source stuff. Based from experience, there's quite a steep learning curve when it comes to creating 3d models using Blender, so I'd recommend allocating some ample time to learn how to use the software.
After you have made your design you can start exporting that to STL files which is the file format that most 3D printers use. Then you can upload that design to an 3d printing outsourcing company. Shapeways is the company that I'm hearing a lot about in the internet when it comes to printing out your 3D models. Haven't tried them yet though so please don't take this article as an endorsement of them. Based however from their active forum it looks like they are a good company to deal with.
You can read up more on their FAQ as to how to go about having your design printed out by them. Shapeways offers a variety of 3D printers and materials that you can have your model printed out on. Which is also something to keep in mind when designing your model as one of your constraints will be the type of material it will be printed out on.
Expounding further on this, hypothetically lets say you want to have something printed out on the transparent detail material that Shapeways offers. This uses an Objet 3D printer which is similar to the 3d printers that Bandai uses when making prototypes of their model kits. The good thing about using this is that you are afforded up to 0.2mm of detail (great for panel lines I suppose) but you have to keep in mind that no part of your model should be less than 1mm in thickness. Also that the maximum dimensions that you can print out is 49x39x20cm. And of course, it will cost you $2.77/cm³ of the said material to be printed out. Then there's the shipping cost you have to factor in also. Shapeways currently ships worldwide by UPS only.
Once that's done and you received your printed out plastic from Shapeways, you can go about making duplicates using silicone rubber molds and resin. I won't go much into detail on how to do that but basically you create molds of your produce using RTV silicone rubber then cast plastic resin in them. You can also read up here on how Model Factory Hiro does it. If your planning to mass produce and sell I recommend investing in the proper equipment for the job, such as a degasser to remove trapped air from the silicone molds for perfectly detailed molds as well as a pressure pot for casting the resin that prevents air bubbles from forming in the resin as well as making sure that the resin gets forced against the walls of the mold to perfectly capture the details of the part. Oh and RTV silicone rubber molds eventually get attacked by the resin, so you could probably get 20 casts out of them before you have to retire those molds. RTV silicone rubber and resin isn't cheap, something to keep in mind also if you plan to do this as a side business.
Well that's how I'd go about it if ever I decided to go into the garage kit or even optional parts business. Check out some Hobby Related items for sale that were created by users at Shapeways. Shapeways functions also like a market place where designs created by users can be sold.
Note: Pictures used in the blog post was of the 1/60 Gundam Exia I built last year and has no relation whatsoever to this post and meant only to beautify this article *snicker*
