How would you bring wealth back to the past?
Edit: A few people have argued that this question is off-topic, and as I write this it looks like it will be closed soon. However, I have written a new (and hopefully better) version of the question at https://worldbuilding.stackexchange.com/questions/114178/how-could-an-inter-temporal-banking-system-work, and I hope that you will take a look there.
Original question below:
Suppose you have a working time machine. You decide to go back 50 years and buy a house; after all, in 1968 the average cost of a new house was just about $15,000, quite a bargain!
The problem: How do you transfer $15,000 back in time with you? Cash, obviously, won't work, unless you somehow have access to paper currency that was printed before 1968. 205
(Not likely: the lifespan of paper money is ~10-15 years, so good luck finding large quantities of 50-year-old cash.)
Maybe you could bring gold back with you? Not a good idea -- gold currently costs about 30 times more per ounce than it did in 1968, so in order to have bring back enough gold to buy a \$15,000 house, you'd need to start with $450,000 worth of gold.
So -- how would you transport $15,000 worth of wealth back in time with you to 1968?
Edited: Many of the answers below are really addressing the broader question "How could you get rich using time travel?" Quite a few of them actually involve transferring wealth from the past to the present, or from the further past to the more recent past. The question was intended to be more specific than that; if it helps to focus, suppose you have a single-use time machine, and that you are planning to travel to 1968 and retire there. The cost of living then is relatively low; you just need to figure out how to get your 2018 wealth back to 1968 in a usable form. "Buy something that's cheap now but expensive then" is a good model, but what, specifically, could you bring and sell in sufficient quantities? 130