This will be based on the minimum limits set by available seller offers on the marketplace and the price of bitcoin, but you should be able to buy as little as 0.005 of a bitcoin (0.5%) or the digital currency equivalent.

Satoshi is the smallest fraction of a Bitcoin (0.00000001 BTC or a hundredth of a millionth BTC). In the future, however, the protocol may be updated to allow further subdivisions.