You can get red lentils , very cheaply, near to the stock cubes usually, there are also green ones, and my favourite lentilles verts which are the same as puy lentils. Try split peas too (yellow or green) and use them the same way. I usually use 4oz for 2 of us, use 2 stock cubes, onion carrot celery sometimes green beans, you can spice it up if you want. I have a pressure cooker so red lentil soup is ready in 8 mins, I suppose it will take about 25-30 in a saucepan. Split peas take 20 mins so probably 45 mins on the stove.
Just be aware that you will be very windy after them!