Minimum thickness, on my OEM rotor, was listed as 4mm. Mine got all scored from a shitty rear bearing, some spots were around 3.5mm.
Ended up being about $230 from a local shop for a new Honda rotor -- way to support the local guy! Pads were cheap, maybe $25?
Real easy to replace and I'm no mechanic. Remove wheel, heat up wheel near rotor bolts (they use red locktite) then take out bolts. Clean wheel mating surface, align new rotor, locktite bolts and torque them in.