As the US and Euro economies unwind and their middle classes fail, we are likely to see the rapid growth of massive "grey market fairs" develop outside most major cities. These grey market fairs will likely be modled on Argentina's La Salada (it's huge with over 30,000 stalls).
This fair has been around since 1991, but saw his most significant expansion after the 2001 Argentina Debt Default, where Argentinean Peso devalued 400% and 5 presidents were overthrown in 15 days. At that point; Argentinean middle class saw the need to acquire clothing and other products at one fourth the price. The fair's yearly revenue grew from under 100,000 the early nineties to 15 billion in 2009 according to the official statistics institute INDEC.
Fairs as big as this will grow quickly as people sell many of the used consumer items from their current middle class lives. As things worsen, it will be a great place to sell new DIY systems and fabricated prototypes -- or -- trade for parts/materials needed to build/fuel new things.
Think about where the fair will be outside the city near you... Lots of business opportunity there.