Indoor cycling vs Winter cycling: Which costs more?

The summer is often a great time for people to get into cycling, with the nice weather, blue skies, big dose of sun and limited cause for punctures or bike cleaning. But for those riders who took up cycling in the summer, and are now faced with lower temperatures, wind, rain, and bike cleaning, there are two options. We can get properly kitted out to keep up cycling through the winter, or take up indoor cycling. 

But with the price of everything seeming to go up and up, what are the costs of either option? Which should you choose? And how can you achieve the best results for lowest cost for each option?

Riding outdoors over winter