99 caravan brake issued

I bought a 99 caravan, brakes always
seemed a little hard to push. Had them
checked and they said if anything they
needed rotors ground to remove some
noise. Yesterday I went to leave and could
push petal to floor, hardly stopped. I have
no leaks that I can see and master cylinder
is full. Took one tire off, took off bleeder
cap and tries pressing brake, no fluid came
out. I know it could be a multitude of things
from airinline,power booster, caliper to
cylinder. Can anyone help me diagnose,I
have cancer right now and cannot afford
the lies a brake shop will give me. Last time
I went to one they tried to get me to pay
$500 for engine mounts saying they were
broken, not knowing i knew they were
hydrolic and we're sopposed to move. I just
don't trust and cannot afford especially if it
something I can do myself.