the biggie in our family has become the 4th of july. Overall, it's probably pretty pricy, but individually it is not. My dad lives on an 800 acre lot in the mountains, and every year on independance day we have a HUGE bonfire/potluck/fireworks show. Everybody brings something to eat, and some fireworks to contribute to the 'pile'. We spend the day with music and a big bonfire, just hanging out with each other. We might go down and swim in the creek, fish, and generally just hang out. Then we eat. Then come the 'daytime' fireworks for the kids (parachute men, cars, etc.) and the cannon. My dad built a black-powder cannon that we shoot stuff like fenceposts, watermellons, pretty much anything that will fit. Once night starts to fall, my dad and the other guys light off the fireworks. We usually have a decent show there, because he built some special 'launchers' for the shells, so our show is just as impressive as the one the city puts on. (yes, he got a permit. lol.) It started out fairly small... just a picnick with my immediate family, but over the years it has grown. Now we generally have at least 20-30 family members, plus friends, plus neighbors and other locals. (it's a small mountain town.) It's something we look forward to every year.
We also have a christmas tradition of having helium balloons in the living room when we wake up christmas day. Tanks of helium are pretty cheap to rent, and balloons are really cheap, so you can't even see the ceiling through them all. :)