This already exists... and it keeps going up.
Sell a def for 4 speed, buy a def for 3 speed until you have enough speed profit to buy 5 def.
Buy a life for 5 def, sell a life for 6 def until you have enough def to buy an extra life.
Buy an inc for 1 life, sell an inc for 2 life. Continue until you have 200 life, sell in the trading section for dat monay.
Keep selling life until you get $100 of dat monay
Trade stocks and commodities until you turn $100 into $200
???
Buy an ipod