This is a simple and easy way to build your money in Kerbal Space Program (KSP) Career Mode without having to mod or alter your game and is applicable to the current version (even if it is modded). Please note that while money will help in your builds, it wont help you generate science which you need to advance deeper into space.
In order for this to be effective, you should start with an initial capital of around 500,000 in funds because were going to use the premise of compounding percentages and a revolving door method. That's fancy speak for "were going to keep doing the same thing over and over till we get a bazillion spesos!" This is just a recommendation since it will take longer at a lower initial investment to make more than a few 10,000 each time around.
Aggressive Negotiation Strategy
Next your going to go to the Administration Building on the far left side of your KSP facility map. Inside you'll see four Kerbals that are eager to help you run your program. We want to use the Gus Kerman (Operations) strategy of "Aggressive Negotiations." Click on it and it will bring up a description and effects on the right. Below that is a slider bar that allows you to divert a percentage of commitment into the program. Slide that bar as far to the right as your current progress allows. Once you get further into the game, have more "Reputation" points, and upgraded the Administration Building you can come back and invest more into the program to pay you more funds when you perform the farming method.
Build, Build, BUILD!
Now you can go to one of two places, either the Spaceplane Hanger (SPH) or Vehicle Assembly Building (VAB). Here your going to build the most expensive vehicle that you can afford. Your only limits will be on the level that you've upgraded both the building and corresponding runway/launch pad since the larger (more parts) and heavier (weight in tons) vehicles will net you faster gains. Once you've built the machine that broke the bank, click on the green "Launch" button in the upper right hand corner and send it to the pad or runway.
That's right, just like the title says, your going to recover the vehicle and not do anything with it. Just slide the mouse cursor over your altimeter in the upper central portion of the screen to bring the drop down menu into view and click on "Recover Vessel."
Rinse, Lather, Repeat
And just like that, you're a little richer. Keep going back to your vehicle building, add more expensive tinkets, launch to the pad/runway, recover vehicle while its on the pad/runway, and collect your funds.
How does this work you ask? Its all thanks to that "Aggressive Negotiations" strategy. You reap the percentage in savings that you commit to by your initial discount in building costs, but when you recover the vehicle un-used, you recover the funds for the full cost of the parts. Its like buying an item on sale, but being able to return the item for full price later.