I have been working out for 15 years and have been working out at home for the duration of that time with the exception of four years in university where I had access to the school gym. Needless to say I knew how to set up an effective home gym without spending too much money and when I was able to spend money, I spent it wisely on the best equipment. If you are looking at starting a home gym but don't have that much money, here are my top three product choices in terms of value and effectiveness. They cost less than $100 and can provide a great boost to your workout routine.

Attachable Chin Up Bar. This bar can be very useful for anyone less than 300 pounds who wishes to work on upper body exercises that use their own bodyweight beyond traditional pushups. The bar latches onto your doorway without having to screw it on so you won't damage your walls. It allows you to perform a variety of chin ups and dips, neither of which can be easily and safely duplicated at home by using standard household equipment. These bars generally range between $20-$50. Be aware that the $20 bars may not have all the features you need to perform dips on them.

Dumbbell Set. A dumbbell set for less than $50 is a great addition to a home gym for beginners on a tight budget.The only problem with a set like this is that it only has enough weight for up to 20 pounds for both dumbbells at once or 35 pounds for one dumbbell. While anyone serious about training at home for weightlifting or bodybuilding will eventually outgrow this set and need to get a home gym or barbells and a bench press, a dumbbell set like this can be a great start for its price.

Hand grippers. Hand Grippers are a great tool for improving your gripping strength, which is key to handling extremely heavy weights during Deadlifts or Clean and Presses. They range from very simple models of less than $10 to more advanced equipment of $25. If you are a beginner, the simple models are probably sufficient for your needs.

Seeing as how you are on a budget, you may have to supplement any potential purchase of items below with exercises that can be done without any equipment or with items found in the home. Refer to my articles on Upper Body Exercises and Lower Body Exercises that can be done with no equipment needed at all.

My workout routines:

How to build big Biceps
How to build big Triceps
How to build big Forearms
How to build big Shoulders
How to build a big Chest
How to build a big Back
How to build big Legs
How to build big Calves

Dumbbell workouts:

Dumbbell Exercises for the Arm Muscles
Dumbbell Exercises for the Chest
Dumbbell Exercises for the Shoulders

More of my workout advice:

Are Bowflex SelectTech Adjustable Dumbbells suitable for you?
Should you buy Bowflex SelectTech Dumbbells in a store or online?
Why you would want to use barbells for your workouts
Why you would want to use dumbbells for your workouts
How I lost over 40 pounds in 6 months with some simple diet changes
Upper body exercises with no equipment needed
Lower body exercises with no equipment needed
Cardio exercises with no equipment needed
The Different Ways of Doing Dumbbell Bicep Curls
Inflatable Exercise Ball Exercises for Men