Last time I bought a PBR rear brake caliper overhaul kit for an EA
Falcon, it was about $37 per side. The fronts are probably slightly
cheaper as they have less bits n pieces.

As for doing the job, piece of piss.
Completely remove the caliper from the car, 2 bolts for the front +
brake line and take it somewhere clean - the kitchen a good spot if
you want to wind the missus up :)
drain all fluid and plug the hole, remove pads and clean the caliper
of all loose dust/crap - to be safe don't breathe the dust in.

Push the slide tubes out, they will pop out of the boots, clean the
tubes up, bit of grease on them and put them all back together with
the new boots from the kit - the slide tubes should move nicely with
no grabbing.

pull the piston out, it should come out with a bit of work, if it
doesn't the piston and/or caliper housing could be pitted which wil
need cleaning up or possibly replacing. the rubber boot will also pop
out, clean the piston/bore - I just use brake fluid and a lint free
rag pop the new boot on the piston and lightly oil the bore/piston
with brake fluid - push the piston back in all the way (a big G clamp
is handy here) and tuck the boot into the caliper, this bit takes a
bit of mucking around but its important to get the boot seated
correctly.
slip the new pads on, bolt it all back up and bleed that caliper.

The above is for the fronts, the rears are bastards but a similar
process. Slacken the brake cable off and remove the hook from the
brake lever, remove 2 bolts + brake line, do the draining/cleaning up,
remove pads and reco the slide tubes.
Note the position of the handbrake lever (I think its sits hard
against a raise block on the caliper.
Undo the bolt holding the lever, there is a rubber disk under it from
memory which will fall out then push on the shaft and make sure your
ready to get the piston as it all comes out as 1 assembly, clean the
bore/piston, put the new O ring from the kit over the rear shaft, wind
the shaft all the way in, put new boot on, oil the rear shaft/Oring,
piston and bore and slide it all back together - take car when the
Oring engages as you can pinch it, tuck boot in etc.
At this point you have to do some mucking around, the piston has a
notch which must sit at the 12 Oclock position (note the pin on the
back of the inner brake pad for reference) and you have to adjust the
shaft until the brake lever sits in the correct position - hard to
explain here but you will work it out when you see how it all works.

When all done, put new rear seal i nbehind the brake lever, put bolt
back on, new pads on and thorw it all back on the car.

Note, I prefer to do a preliminary bleed of each caliper after I bolt
it back on as you have less chance of draining the master cylinder.
Once all 4 are done, do a final bleed starting with the back left,
back right, front left then front right.

jesus, I think I wrote the manual here :)