An experienced developer can make an extremely simple game in a day, or a week. An experienced developer can make a relatively "simple" game in 3 to 9 months. Since you have to ask the question, you have to learn how to make a game - no telling how long that will take. Then, since the code you made while learning probably can't be used, an optimistic guess would be 3 to 9 months additional.  

Depends on your training skill, and available time.

If you want to experience making a game quickly, I can suggest you go participate in a game jam.

It is a very good experience in how you can make a game over a weekend.

(Mainly in how to aggressively cut out features so that you can deliver a finished "product" )

Are you aware of, or have you participated in any game jams?

A couple of popular ones are Ludum Dare, and Global Game Jam, both of which take part over a weekend. Keep in mind that the expectation is that these games are shorter experiences and aren't necessarily feature complete, but take a look at some of the games people are able to produce in that time frame.

Really, the answer to your question depends on a number of factors including your definition of 'simple', your level of skill, and the amount of time you're able to put in.

Hope that helps!

13 minutes ago, Timothy Sharp said:

How much money are game jams?

It depends on the jam.  Many of them -- especially those done online as Ludum Dare is -- are free to participate in.  Others may charge a small fee to cover any costs associated with the event; in-person ones, for example, may need to cover the costs of facilities, electricity usage, etc.

If you're interested in taking part in a jam, this calendar lists many of them - just check the web pages to see if there are any special requirements or costs involved.  I mostly mentioned them to provide an example of what developers can produce in a very limited period of time, but I do also highly recommend giving them a try.  

If this is your first one,

I really recommend doing the "in person" one. So that you can actually see how other people are working.

I would only recommend the online ones once you already know how to work.

Personally, I really like my local Global Game Jam. It's also cheap (15$) for the weekend. However the entry price is totally up to your local organiser. Some sites charge more, and some are totally free.

The only downside is that it's usually organised in January, so you have a long time to wait.