Sure there are a lot of great training aids out there and many of them can greatly improve your golf game, but sometimes funds are tight and you really don't know if the training aid is going to work for you.
Here's a free training aid you can make in your home, assuming you have some scrap wood laying around, to improve your putting. One of the many reasons that people miss putts is due to SDT or "Sudden Deceleration Trauma." You know, when you take the putter back too far and realize it as you are about to make impact on the ball so you slow the putter down or worse stop it right at the ball. This training aid will help you develop a more fluid and consistent stroke and path through the ball.
First, get a 2x4 or similar size piece of wood. Use a saw to cut it down to 2 feet in length.
Next, find the center of the 2 foot length. Using a ruler and magic marker, draw a line widthwise across the board. (See pictures below.)
From this center line, measure and mark 4" increments to the end of the board in both directions. You can use a coin or other circular item to make a circle in the middle of the center line.
Now place your new, fancy training aid on the putting green. Align your putter to the mid-point of the board and practice taking the putter back to one of the lines and follow through to the line the same distance past the center point. Do this until you consistently start and stop on the same line on each side of the center point.
When you are feeling confident in your stroke, line the board up so it is aimed directly at the hole. Drop a ball at the center line and practice the same stroke with the ball. Don't worry about getting the ball in the hole, instead focus on creating an equal length pendulum stroke with your putter.
After you've developed a consistent stroke, try to make the putt or, as in the putting ladder drill, try to get within 3 feet behind the hole.
And, there you have it! A cheap training aid that will not only improve your putting stroke path and consistency, but also eliminate the dreaded SDT.