The short answer is "probably not".
"Best and cheapest" are contradictory terms.
The idea of insulating a basement seems a little silly at first because it already has insulation: 15 feet of dirt. That provides way, way more insulation than 6" of fiberglass. If the basement is fully underground, "insulation" would be pointless (unless you have some unusual condition, like a glacial underground stream running in direct contact with your wall or something like that).
Nevertheless insulation does make sense if part of the basement is above ground, especially if it has windows. Any kind of window in a basement, that's where your heat loss is going to occur. The heat loss through a window will be hundreds of times greater than through, say, an 8" concrete wall.
So, if you are looking to economize, the best practice is to just focus on the windows and doors , that's really the only area where you can have major heat transfer. Remember, its all about the RATE of heat transfer per unit area. So if you have 400 square feet of wall transfering heat at 1 Joule per hour, its meaningless compared to 10 square feet of windows and transfering heat at 500 Joules per hour.
The easiest thing to do is brick up the windows, 12" thick, with some insulation inbetween, but then, of course, you have no windows. One alternative is just to grout plexiglass or glass over the opening (make sure it is airtight). The more panes you add, the more insulation you get.
Cellar doors, like storm doors, are harder to insulate. The cheapo option is to get a couple bales of fiberglass insulation and just duct tape to the outside of the door (this assumes you have a outer bulkhead door). You can't use the door in the winter obviously if you do this. When spring rolls around you throw out the insulation. Repeat every year. You can add weatherstripping to a door, but in my experience it does not do too much.
If you really want to start insulating walls, you can, but truth to be told, it will not do that much if the wall is below ground level. All your heat loss goes through windows and doors, anything that has a short pathway to the outside air (or water).
Brief Note about Water
Water, by the way, is bad. It will transfer heat INSANELY faster than air, so if you have an underground cold stream in contact with your basement wall, it will wick heat INSANELY fast. You can tell because if you touch the wall it will be freezing cold compared to other parts of the wall. An IR temperature detector will do the same thing. If you have this situation, you definitely want to use heavy insulation on that part of the wall or floor, because it will just suck heat out of the house. This is a rare case though, most people don't have cold streams.