The question you'll have to figure out how to answer is then: how would you pay back $100,000 and in what time frame? Think about the other side. As someone with $100k, why should I chance it with you if the reward doesn't warrant the risk? Angel investors are just that: investors. They would likely put the money into a situation that is less risky.

Also, the number of people in the market is only an important metric when you also include what kind of conversion rate you can get of those, and what dollar amount would the average sale be? Take Ford and Lamborghini. One makes a lot of different models that cover a large portion of market possibility and sells a large number of cars at a small profit, while the other has few models, sells a much smaller number of cars, and has a higher profit per vehicle. If each customer nets you $100k, and you can get 0.1% of the possible market, then of course it could be worth an investor's time. If this is a web app you want to charge $2 one time for, then even if you could sell the whole market it may not be worth it.