The answer is depend on your financial situation, if you are well-off, you can invest it more, otherwise less than as you can. You can buy 1 BTC or 0.1 BTC or even 0.01 BTC. Of course, if you invest a lot, then get more profit or get loss more. But according to current trends, although the quality is few, but its value is not small, it could be multiply thousands of times.
His financial situation is 14$, you could see that in opening comment. More money is always better, I agree with that but most of us started with much less. Its possible to make some moneybwith 14$, risk with some altcoin under 1$, now prices are dropping and I belive in recover and rise, with ripple and iota I earned a lot, I bought under 50¢. Now stellar and cardano have chance to get to 1$ and more. With more money its easier, but its possible with little to make a lot if you catch a good train
Good luck my friends, don't miss opportunity to buy and earn in the future.