Buy new or use what I have

Rotors will be ok, just remove the surface rust on the flat areas where the pads contact. Your biggest concern should be those bearings...
Wipe and clean old grease from inside rotors and spindles.
Clean bearings with Brake Clean spray until there is no old grease on them, dry them good and inspect them for pitting or any marks on the rollers... Re-Pack each bearing, be sure to get the grease in between each roller by pushing fresh bearing grease from bottom to top, Using the palm of your hand or a bearing packer. Trying not to spin the bearing while packing. Wipe your greasy hands on the clean spindle, just a film is good. Same goes for the bearing races inside the rotor.
There's plenty of reassembly tips if you search this site, no need to go over that, again.
Good Luck!