How much does it cost to care for and buy an aquarium?

ok i want a freshwater tank that will hold 5 to 7 fish how many gallons should i get and how much will that cost. what are some popular fish to put in freshwater tanks and what are other cool fish to put in it and their cost. how much will pebbles plants food and areator. please tell me any other supplies i will need. how hard is it to care for this type of aquaruim to care for on a scale of 1-10 10 being the hardest. thanks