Set of four top-quality 15w 8ohm head rest speakers.
Enough to do both seats, these are a very cost-effective solution to worn out speakers.
They do not fit into the original mounting cups (due to the size of the magnet) you can either cut the mounting cups OR just install without them as they fit nice in the cutouts anyway.
Obviously, these are only compatible with models already fitted with the headrest speakers (cover unzips to reveal)
or you will have to run wiring through the seat.