nobody will buy your idea, hire a coder and let them code your idea
Not really true people buy ideas on kickstarter all the time
I think you are misunderstanding what "buy an idea" means. When people are on kickstarter, donating money, they are donating to the cause. They aren't really "buying" anything (although usually there are freebies given in return for certain donation amounts).
On the contrary, buying an idea would be like saying "I like your idea for how a brand new
DevCoin crypto currency should work. Because of this, I will buy the entire idea off you." This means that you are permanently walking away from the idea of being able to create another thing like it (usually they include things in the contract like a non competitive agreement, meaning you can no longer use the idea to make another business. Sometimes this is not permanent -- set for a certain number of days or months, to allow them to be the first to market it -- but most of the time it is).
Donations (such as on kickstarter and other sites that are like it) work differently. Rather than you truly owning anything, you are allowing the person or company to use your money to bring their own ideas to life. This means that they own the entire idea, despite you (and others) doing all of the funding for them through the use of crowd sourcing. I will be honest... I still have no idea how kickstarter is doing so well. There are many things there that people pay for where they barely get anything in return, while whoever is requesting the money has the chance to make it big. It just seems a bit off to me.
If you were to earn a percentage of the company ("stake") as a result of your monetary contribution, that would be classified as buying into it. You will would not be buying the entire thing, and most of the time the owner or owners will keep the major controlling share of it, allowing them to make all of the important decisions and such.
Now, if you were able to buy controlling interest in the company or idea, that would be "buying it."
I also want to add that ideas really do not have much value. Everyone has ideas. The hard part is actually implementing them in a way that works. You can have the best idea in the world, for something nobody else has thought of (which is pretty rare, really. Most things have been thought of before but have not been followed through on), but if you do not have the ability to get the masses aware of the idea, it will not go anywhere. And even if they do become aware of it, there is also the problem of getting them to back it (purchase or use whatever you are creating). Because of this, there is a lot more to an idea than just thinking it up.
There are, of course, some ideas that take off quickly. If you can truly think of something that is not only brand new, but also benefits the majority of people in a way they can understand (and at a price point they can accept), the idea can skyrocket. The problem behind this is that the idea maker is, in most cases, not going to get much for their efforts. In a lot of cases, they will end up "leasing" the idea to someone else that has the ability to make it a reality and get it out on the market, and they will take a small share. This will usually be only a couple percent of the income, but it can add up pretty quickly if whoever you leased it to has the proper know how and connections. I always say "a few percent is better than nothing." And the best part about doing this is that you get to keep all rights to your idea. More or less you are just renting your idea out (so you do not lose it) to them for a specified period of time, and after that you can try to re-negotiate a new contract or use your money to continue on things by yourself. If you do this, it is important to do a non competitive agreement, otherwise if you choose not to re new the contract, the company will be able to continue producing like products (they can not be a direct copy, but the company can produce very similar things).
If you really have a good idea, like the OP thinks he does, the best thing he can do is to rent it out. This gives him full control over it should he decide to go on his own (as long as the contract is expired), while in the mean time obtaining rewards while not having to take part in it anymore (which can be used to fund future ideas or adapt the current one).
In relation to the idea of kickstarter, the reasons above explain why I do not quite get the point of it, nor why it is so successful. I understand the prospect of “crowd sourcing” to obtain money, but I have a hard time following why people would choose to throw their money into a project that may or may not make it, without even getting a big enough share of it (any at all, really) to make the risk rewarding. Even if someone there ends up raising their requested amount of capital, there is nothing that ensures they are raising the right amount. For example, a lot of businesses that go for funding ask for a certain amount, and then in the future realize that they were not even asking for what they needed. I have no idea what would happen if a kickstarter campaign was fully funded and ended up needing more money than they got, but I see it as a big risk with such a little reward. Sure, discounted final products (or early releases) can be good, but when deciding if to put money on the line or not, I do not see the point.