Will a moderately attractive person who thinks he is very attractive be attracted to a moderately attractive person like he is or to an extremely attractive person like he thinks he is?

The answer to this tends to vary, as beauty is subjective. Who you may consider extremely attractive, someone else might only consider moderately so. On the other hand, someone that person might find cute, you might find average. There are other things apart from looks that can add to and diminish a person's level of beauty, such as their personality. A prime example of this is Marilyn Monroe, who is rather pretty looks-wise, but whose level of attractiveness is increased several fold due to how she portrayed herself on and off screen.

With that being said, under the hypothetical circumstances where beauty is absolute rather than relative, a moderately attractive person who thinks he is very attractive would very likely be attracted to both these ladies, as both had been described to have a degree of attractiveness by you. However, this man would most likely go after the more attractive one, if one were to assume that he has the confidence to back up his "good" looks. If he doesn't, he might go after the less attractive one out of intimidation.

However, because beauty is not absolute, but instead, is absolutely relative, regardless of how attractive this man may find his partner, you just might end up disagreeing.