The best and by far the cheapest way to make good coffee is with a cafetiere. It will produce much better coffee for a fraction of the price of any of the fancy-pants machines. These are available everywhere for less than £10 pounds......more if you want one that looks nice of your kitchen window sill !
If your coffee is bitter, than perhaps you are using boiling water. Its sounds counter-intuitive but while boiling water is perfect for tea, it make bad coffee, as you are scalding the coffee grounds. Boil the kettle but let it sit for a minute or two, and then use the water.
Also there are different coffee for different tastes. Some are stronger than others. Personally "mild" coffee is a bit like mild cheddar...what's the point !
So you can explore the world of real coffee for very little outlay. I am in my caravan in Cornwall for the month and I use a small cafetiere, which cost £5:00 in Tesco. My favourite coffee at present is the Viennese Blend from Sainsburys, which has fig extracts added, although its getting harder to obtain in their stores. I changed over from Nescafe Gold Blend about 5 years ago and now no longer buy instant coffee. I also refuse coffee in other people houses, unless I know its provenance !