Run the net price calculators for some of those private eastern colleges and if they make sense, explore some of the smaller liberal arts colleges. Williams has one of the most highly regarded undergraduate math departments. It won’t show up in any of those Math surveys because those are mostly based on graduate school rigor and faculty publishing, neither of which are important at the undergraduate level. Liberal arts colleges mainntain their positions largely because of the level of classroom teaching. Wesleyan is very similar to Williams in educational philosophy, is slightly larger and does have a small PhD program in Math (mainly, Topology) which comes in handy should your son burn through all the intermediate level courses available.