Oxford University researcher Max Roser charted the declining price of lighting in the United Kingdom since the 1300s:
Electricity, from J.P. Morgan's living room to yours
As the above chart outlines, the first major decline in the price happened in the 1800s, when candle production costs dropped thanks to new source materials (see candle price chart below, taken from Seven Centuries of Energy Services, published in The Energy Journal and available on OurWorldInData):
In 1880, Edison found an investor, J.P. Morgan, to help him to convince the public of the benefits of mass-produced electricity for the purpose of lighting. They put on a show with Edison's magic lightbulbs at Morgan's house, famously wowing thousands and, soon after, the nation (read the full version of the incredible story over at PBS):
J.P. Morgan hastily provided the 31-year-old inventor with the capital he needed to carry out his daring scheme. When the first electric lights cast their golden glow over Menlo Park on New Year's Eve 1880, a crowd of 3,000 people gathered in awe. Edison, the worker of miracles, had triumphed.
Electricity is very cheap to buy in most Western countries these days, but it wasn't always that way. For example, take a look at the average price of electric energy in the US between 1902 and 1930, via the Institute for Energy Research:
Electricity isn't available everywhere: about 1.4 billion people live without access to grid-based electricity today. This means there's still an enormous unmet demand for new options like LEDs and solar-powered technologies.