I don't know what the degree fees are for your local bodies (heck, I don't even know what they are for my local bodies!), but, unless you have been officially told otherwise, I suspect there is no difference doing them individually or in a festival.
Dues are different at each Chapter/Council/Commandery. I can tell you what mine are. The Chapter and Council are $16 each. The Commandery is $35. By comparison, our Blue Lodge dues are $64. I suspect the ratio is similar in most places. (I am a life member of everything but the Commandery and do not receive dues notices, but I'm certain those are the current prices).
You are under no obligation to join all three bodies. You can join just the Chapter, the Chapter and Council, or all three. I personally wouldn't recommend breaking up the Chapter and Council. They go hand in hand in terms of the story and most meetings. For example, my C/C meets on the same night. We open the Chapter, conduct business, close, open the Council, conduct business, close.
If money is a concern, I'd honestly not worry about the Commandery. The story does nothing to further you Masonic education as far as the Hiramic legend goes. I actually demitted out of the Commandery for about 10 years because of financial reasons but rejoined when we formed a local Commandery. I know you have expressed concerns in other threads about the cost of the Commandery uniform. Unless your local Commandery has some kind of rule about it, you do not have to have a uniform to attend meetings unless you are an officer. That said, if you do become active, you'll want to have a uniform.