Elaborate a bit more about your idea, being transparant is a good idea, there are ways to 'lend' bitcoins to start something.
You need to convince the ones you want to invest. This means you have to invest in promoting your idea. When giving away there is no ROI other than the long term effect it might have on BTC acceptance, it is a long shot and not many are willing to pay for that.

The amount should not really matter. You can start a service for which you can pay with the given BTC and prove users how easy it is to send and receive bitcoin payments. This means not only giving bitcoins and a wallet to store it in, but a total experience.