1) Designing Your Invention (CAD Software):
A) If you just want a shell of your invention, then learn to use Rhino3D, or some other 3D design software.
B) If you want to have the entire mechanical internals of your invention be a part of your prototype, then use something like Solidworks which has a physics engine to be able to simulate actual mechanical functions.
2) Showing your invention (3D Rendering or 3D Print)
A) After designing your invention in the CAD software you can now make very realistic looking 3D renderings of it (if done right it can be made to look like a photograph of a real thing). You could use these renderings in an indiegogo campaign or demo video or pitch deck.
B) You could also print your design as a physical 'thing' that you could actually place into investors hands. To do this you could buy your own 3D printer, or use a company like Shapeways which will print it for you in your material of choice.
Alternatively, you can collaborate with a freelancer do help you with those steps.
If you'd like more specific advice tailored to your unique invention, or if you have other questions about the early startup process let me know,
This is not a DIY project. I strongly suggest you go straight to a product designer/industrial designer who has been there and done that before. Not only will they be able to get you what you need for prototyping and possibly 3d Printing if it is right, but you will insure that your product is engineered to be properly and efficiently manufactured so it can cost out as well.
Getting into some fun stuff are you. Anyway, you can download software here https://www.autodesk.com/products/autocad/overview and they also training courses on how to get start and so forth. Apply for a student license, if your not a student at a local college, look in your area and say you are. The real truth is if you are learning autocad you are a student.
the answer is a little bit late maybe :)) but i still wanted to reply..
The most common mistake by the start-ups are the ambition to do everything by themselves. Being cost-effective shouldn't mean "doing everyhting, in-house or on your own". Spending right amount of money on the right source can make the process more smooth and can help you focus on the correct target as well.
If you are a start-up, don't think that everything counts on only money. Be creative and create alternative business models, which still keeps win-win situation. For example, instead of spending a bulk amount of money on developing a prototype or creating a pitch video for crowdfunding, propose a smaller amount of down payment until the project successfully launched and then give more money or shares as a compensation. I'm quite sure that you will find some professional who are interested in your ideas and can accept this kind of business model.