Is it appropriate to include dollar amounts for awards granted when applying to a math PHD?
It is entirely your choice -- doesn't hurt, but not necessary either.

Readers of grad school applications generally have a decent idea of how much REU or travel grants (a couple of thousand dollars) and how much departmental awards are worth (a few hundred dollars, typically). So not stating a number is not a big deal. Stating a number also doesn't hurt: if it's within the range a reader would expect, then there is no harm done, space is cheap; if the dollar amount is surprisingly large -- say, a $5,000 award for your work, then that's useful knowledge and should have been on your CV indeed.