Question: Are you looking for an angel investor, or has one approached you?
If you are looking for one and have no contacts then I don't think there is really an answer to your question, but somewhere close to zero.
However if someone has approached you then that is a different question. I've talked about ideas in the past and had people ask me about investment. The way I value that is if I am going to work the next five years at startup levels of stress and hours I value my income at US$200,000 a year. So five years (commitment I would assess putting into it) x 200K is $1,000,000. Then it is up the investor as to what percentage they are after. So 10% means I would want them to invest around $100K.
That all needs to be balanced by your level of experience, financial expectations, how much you need the money - and how likely you perceive the potential to accept the concept.
If you are looking for one and have no contacts then I don't think there is really an answer to your question, but somewhere close to zero.
However if someone has approached you then that is a different question. I've talked about ideas in the past and had people ask me about investment. The way I value that is if I am going to work the next five years at startup levels of stress and hours I value my income at US$200,000 a year. So five years (commitment I would assess putting into it) x 200K is $1,000,000. Then it is up the investor as to what percentage they are after. So 10% means I would want them to invest around $100K.
That all needs to be balanced by your level of experience, financial expectations, how much you need the money - and how likely you perceive the potential to accept the concept.