I think you can buy large foam pots at Lowe's or HD. They'll be expensive, but a lot less than $500 :)

Otherwise, you could try cutting a plastic garbage can so it's shorter. Don't know if that would be cheaper. Long ago, when garden centers were less available I planted a Ficus in a cut down plastic garbage can to get a pot big enough. It worked for more than a year, but the roots eventually split the "pot".

Or you could try one of those "grow bags" they have for veggies. I've seen some really big ones in catalogs.

About watering-- no one can tell you that exactly because so much depends on your own situation, how much sun and air, how big the pot. Just make sure your pot has plenty of drainage holes. As the diameter of a pot goes up, the volume of soil the pot holds goes up by the *swaure*, so big pots can get waterlogged easily.

Make sure your pot is not *too deep*. Use a very porous mix that drains fast. Make some extra holes in the bottom of your pot with a soldering iron. Then make sure the water you give is relative to the sun and wind the plant gets.

Outside in full sun, on a hot and windy day, watering every day might not be too much. Inside in winter, watering once a week might be too much. Use the rule "more sun, more water and fertilizeer", "less sun, less water and fertilizer".

Good luck.