Currently there is no fee you have to pay to ManIQ, however, in case the project is successfully funded, you are kindly asked to transfer your mentor their fee, valuing their effort and collaboration.
As far as the project costs are concerned, we would suggest you browse the internet, ask friends, enquire at companies regarding the potential costs of your project (e.g. the production of a robot), and having all this information, give your target amount wisely. A lower amount may not be enough for realizing your project, and a much higher amount may sound irrealistic to people, and they might decide not to donate.
Doing your calculation, you should also keep in mind that PayPal charges fees to the person who receives the donation, which varies between 3 and 5% of the donated amount. (For further info please visit the Paypal website: https://www.paypal.com)