Why not earthworms? They are cheap, easily available from bait stores and easy to keep for several weeks at once. What about waxworms? They are nice and softbodied (but very high in fat, if I remember correctly).
:grasshoppers ( assuming i could get :clean" ones)
I don't think they eat hard-bodied insects, but I would try a captive raised cricket before I brought a wild grasshopper in.
:red-backed salamanders maybe?
Possibly, but why take wild red-backs out of the wild to feed it? There are several captive raised alternatives.