Those three things are tempered by your goals and choices: Do you want to grow just a little for you and maybe a small family, or do you want to have a setup large enough to sell at a market? Do you just want to grow low, bushy plants like herbs, lettuce and greens, or do you want to grow taller plants like tomatoes and beans? Do you want to build or buy a greenhouse for your plants, or do you want to grow inside your home? Do you want a ready-made system, or are you able to build your own system? Are you comfortable with chemical-based nutrient solutions, or do you prefer “natural,” or “organic” solutions?
There are hundreds of answers and choices! It makes it difficult to get started when there are so many ways and ideas about growing plants in water. My point is this: Evaluate your skills and abilities first. Do as much research as possible. Seek advice. Then decide what you want to grow and why. Only then do you need to be concerned about the cost and complexity. If you have little or no skills in growing anything -in soil or water- then you don't need to be wasting time and money on expensive and complicated systems. You will be incredibly frustrated! You might as well donate your money to charity or buy something for yourself; it will make you feel better.
Start with a basic passive wick system, learn about hydroponics, and then expand and try different things. “Grow in knowledge; grow well.”
Here are some links for major hydroponic systems. I'm going to give a short synopsis of the Plain 2 Grow System Hydrosock passive wick way of growing, and everything else will have links to other growers and suppliers. The Plain 2 Grow Jim You Tube channel has dozens of videos from other growers that cover all aspects of the major systems. The web and You Tube makes hydroponics pretty simple.
types of hydroponic systems - Google Search
What is Hydroponics?| Six Different Types of Hydroponic Growing Systems | Hanna Instruments, USA
You'll want to explore these systems, listed in no particular order: Deep Water Culture, also called “DWC.” Nutrient Film Technique, or “NFT.” Aeroponics. Passive Wick. Ebb and Flow; also called Flood and Drain. Aquaponics. Vermiponics, also known as “Wormponics.” Run-to-Waste. Fogponics. Bubbleponics.
When you watch my videos, you will see that I have used several different systems, and combinations of those systems. The easiest and cheapest one is passive wick. One of those videos, shown on my Plain 2 Grow Jim channel and on my Plain 2 Grow Systems website, uses passive and active wick, deep water culture, nutrient film technique, aeroponics, and bubbleponics in one reservoir! What I designed was just one of many hybrid systems that others and I have created. It is simple to make and very inexpensive.
The Hydrosock passive wick system is super-simple and easy-to-make. A cotton-rayon gym sock is suspended inside a one-gallon plastic milk or water jug. The sock is filled with perlite and a Jiffy sphagnum peat moss pellet containing a germinating seed. The jug is filled to about one-half gallon with a nutrient solution made from water and General Hydroponics Flora series liquid nutrients. A cheap aquarium air pump aerates the nutrient solution. I have grown at least four different tomato hybrids, peas, beans, sweet banana peppers, bell peppers, collard greens, and a watermelon (it grew well but didn't fruit) from the Hydrosock. I've picked hundreds of vegis and fruits! The Plain 2 Grow Systems Hydrosock is a great beginning system!