Once you have the prototype, find a factory that can make it for you as competitively as possible. By now, you will have gone through several iterations of the part and you can write up and submit the provisional patent. You can use the www.uspto.gov site and the Google patent search at https://www.google.com/?tbm=pts . You now know what your final product is, how much it will cost to make in volume and now the real work begins.
Now that you have a working prototype, with a patent pending number on it and hopefully some marketing literature and video, get yourself a independent rep that works in that industry to find distributors and wholesalers and try to get a mutually exclusive contract with them for one to two years, where they can’t buy a competing product and you offer them an exclusive territory as an authorized exclusive distributor. For this right, they must buy a minimum quantity , usually the same minimum that your factory requires. I would sell the part to your distributor at double your landed cost. With the p.o. and contract from your distributor, your provisional patent and a quote from your factory in hand, you can make a trip to your local bank for a line of credit. With the loan, you can buy your product and have the money for the full patent.
I want to emphasize a few points. If it is a unique product, the most important thing you can do is get the right partners and get it to market first. Start doing the research on as much in the beginning as possible. Including on how to write the patent and selecting the best Rep. You will only have a certain amount of time from the time your provisional patent gets approved before you have to get real patent or it will expire. In my opinion unless the product is revolutionary, the process of getting a provisional patent is the most important part so that even if you don’t get a full patent, at least you can prove prior art and no one can file a patent to keep you from making it. Most importantly, remember I am not an attorney, so verify everything I mention and that everyone else tells you as well.