What else is out there that is comparable to these that cater to gifted kids?
AOPS (it has been discussed on this forum a few times).
IMO, both EPGY OE math and AOPS are excellent, *IN DIFFERENT WAYS* (I do not have first-hand experience with CTY). EPGY OE math is 'standard' math (one is taught standard steps for standard problems), while AOPS is all about problem solving skills, where one is supposed to figure out steps (or various best sequence(s) of steps).
Example AOPS (prealgebra, chapter 1, arithmetic): something like: calculate 95+96+97+98+99. There are a few solutions, besides straight addition, among them:
1) 95=100-5, ... (and then add -5+(-4)...)
2) apply formula for arithmetic progression - directly or (better) extracting 100s first.
In addition to textbooks (about $35), AOPS has Alcumus (online problem and solution engine, free) and (lively) online session-based courses (about $250 for 16 weekly sessions). Course cancellation period is 2 or 3 weeks, which is very useful for deciding if a particular course would work for you.
For math before Prealgebra, AOPS has (newer) Beast Academy, with which I am not familiar, but which has been disussed on this forum too.
BTW, AOPS is the home of a famous (very short) article "Calculus Trap" about (in my words and I apologise if I get it wrong) 'new content' consumption (which maybe too easy (= bad) for gifted children) vs. hard problem solving.
