I agree it is frustrating, but PhDs and AuDs are very different things, and the funding comes from very different sources.
PhD's do the bulk of research (i.e. work) on federally funded NIH R01 and/or similar grants, and most often that is where their funding comes from. It trains them, but they are also publishing research, contributing scientifically to the field, etc. Professional degrees (AuD, MD, OD, JD, etc..) are typically not funded through these means (we aren't doing major research!) and funding has to come from individual departments or schools/universities. You are better off comparing funding scenarios between AuD's and other professional doctorates, as opposed to AuD vs PhD.
NIH does have some funding for dual degree AuD/PhD's if you do them in tandem (similar to MD/PhD funding), if you are interested in research!
Additionally, NIH has generous loan repayment programs where if you are doing 20 hours a week of qualified clinical research and have a doctorate (AuD), they will repay a quarter of your loans (up to like 60K a year I think) per year for up to four years! I know someone who is using his PhD research (that he working on after the AuD) to repay his AuD loans through this program.
There are also federal loan forgiveness programs that AuDs can fall into, depending on what settings you ultimately work in.