Where do I find the funding information for each math PhD program? I will be applying for math PhD, and was wondering if there is any way to find the amount of stipend I can get for each program (already checked each school's website, without avail). Are top 50 math PhD programs generally fully funded, that I shouldn't be worried about it too much?
In the US almost all doctoral students in math are eligible for either a TA or an RA position, but mostly TA. The universities require a large number of TAs to manage the undergraduate program so as to free up professors for research and doctoral advising. Funding is modest, and 1/3 or so of your time might be spent on TA duties. Tuition is also normally waived for TAs.
Some professors might have funding for an RA or two, but there would still be duties.
But for those wishing a career in academia, starting out as a TA gives you some experience on the teaching side, if only (initially) grading and holding small tutorial sessions. An RA would be more valuable for someone wanting to go into industry, but they are not as common, and likely much more competitive.
There are relatively few positions that have no duties attached. At one time there were widely available federal scholarships under the National Defense Education Act but those ended long ago. A few, more tailored, programs remain.