Ammo box
If charging a LiPo goes wrong it can have serious consequences if you do not take action on time.
But fire can not go anywhere in an ammo box and will not burn your house.
Ammo boxes can be bought on Ebay for around $30
LiPo bag
A lipo bag is fire inhibiting, after a while the bag will also burn.
But in most cases you have enough time to take action.
LiPo bags can be purchased from $2 but I would not trust them.
Buy one at the local hobby shop.
Bag of sand
This is probably the safest way.
You put the battery in a bowl and close it with a big bag of sand.
If something goes wrong, the bag melts through the heat and the sand falls on the fire
That will ensure that it goes out.
here is a video:
This guy made it for $20