I've looked through several options, and am speaking specifically for my situation.
Since my parents had their own dark room back in the 60ies, I have most if not all the gear already available (enlarger, tubs, trays, cutter, etc). The cost will go into the chemicals and paper.
You will need several different types of chemicals ranging from 10 to 20$. If you want to develop colour, you will need a different set, unless you're into the trippy cross-processing but I am getting off topic a little,.
depending on the type of paper and specific LOOK and FEEL you are looking for (cotton, matt, glossy etc) packs of 25 sheets can range from 25$ to well over 100$. These are special photosensitive papers, not the same you would use in a printer.
It is also very important to note that you can only develop Black and White in a red light environment as B&W film is only sensitive to Green and Blue. For colour, you will need TOTAL darkness, the slightest of light leaks could break and entire roll. So you will need experience.
All in all, for me, it costs more to develop on my own than to just Process the film and have the rolls burnt on CD (Again, prosumer scanners would give sub part quality compared to having a Lab burn it on CD for you), then having them printed out for 25¢ to 67¢
You wouldn't develop for cost saving, you would develop for fun, control and experience gain.
If you do decide to go the route of building your own dark room, here are some links for you:
Quick start Guide:
How to Build A Darkroom
Materials:
Darkroom - B&H Photo Video
Remember, those labs develop a good amount of pictures every week, enough for them to afford having a low cost as they buy in bulk and have big machinery (well, those that I have seen are twice the size of an office photocopier) which makes processing MUCH faster. However, not all labs are created equal and if you wish the Process and Develop black and white film, many labs have to send your rolls out as the chemicals used for B&W are different than Colour.