I've seen several comments / price listings on re-built calipers lately. You can rebuild these yourself; if you haven't done this before you shouldn't be too intimidated. Rather than blow $100-$200 on rebuilt calipers, you can usually do this yourself. I've personally rebuilt hundreds (well, maybe not hundreds; at least tens) of calipers. Mostly you just disassemble, thoroughly clean, and re-assemble. Exceptions to this are cases where the piston had to be replaced either because of rust/pitting or because the OEM was trash (Chrysler used to use these funky plastic pistons, they were so problematic we always replaced them with metal ones).
I would not do a brake job without servicing the calipers. You must keep in mind that brake fluid absorbs moisture, so corrosion is almost always present. Also, when you force that piston back down the bore it often damages the seal, so you either have a leaking caliper or at least it doesn't move as freely as it should-i.e. it drags slightly. This will drastically reduce pad life and encourage rotor warping.
The following is the methodology I've used for 15 years. It may not be suitable for all sorts of vehicles or brake systems. IMHO, FWIW, YMMV, etc.
To rebuild you own calipers, you'll need the following supplies:
Generally follow this procedure:
Get the calipers off the car, and drain the fluid out of them. Also, get all the grudge off of them. Keep in mind cleanliness is next to godliness here.
Disassemble the caliper. The method I've always uses is quick (and sure to surprise anyone nearby!) Clamp the caliper in a vise, put a 1" thick piece of wood in the opening where the pads / rotor normally are, put several shop towels over it and CAREFULLY apply air pressure to the caliper. NOTE I SAID CAREFULLY!!!! Normally, the piston will slide out with a "POP" and your done. If, however, it's badly gummed up it will resist, which will result in you're building up quite a bit of pressure and when it does come WATCH OUT! If you've got it covered and you're careful you'll be fine.
Thoroughly clean everything. Using the alcohol and the sandpaper clean the piston and inspect it. If after cleanup it's surface it not perfect (no pitting, flaking, etc.) discard it and replace. Clean out the bore of the caliper in a similar fashion. Pay special attention to the groove that the seal and the dust boot go into. Use an wire brush to get these cleaned out. Make sure the face of the caliper that the outer pad rests against is clean as well .
Now is a good time to remove and clean-up the bleeder screw, and make sure it's open and working properly. Don't forget this- nothing sucks worse that doing all this, getting it back on the car, and then twisting off the bleeder screw because it's frozen!
Make sure everything is clean an dry. Be sure to rinse everything with the alcohol so no debris/grit remains.
Lube the seal with the assembly lube and install. Make sure it is well seated in the groove.
If the dust boot fits in a grove, install the dust boot in the caliper. If it has a metal collar and goes in like a grease seal, install it on the piston.
Lube up the piston and slide it in. If the dust boot is already in the caliper, it can be tricky to get the dust boot over the piston, they often want to slide off. You may need to use something to help it on, like a small dowel rod, a Popsicle stick, whatever- Just make sure it's clean and doesn't have any sharp edges that will damage the dust boot. If you have the sort of dust boot that has a metal collar on it, you'll need to tamp it down after slipping the piston in. A seal driver makes this easy, but you can normally do it with a small mallet if you are patient and careful. When you're finished you should have the piston seated, new seals, clean threads, etc.
Make sure any machined edges that the caliper rides on are clean, and any guide pins are clean also. You'll want to lube these with a lithium grease.
Reassemble the whole mess.
Brake fluid will eat your paint, so be careful not to spill / splash /etc.
Don't use anything but assembly lube made specifically for brakes, or brake fluid. If you use any sort of petroleum based lubricant it will attack the rubber (BAD),
Use fresh brake fluid. Use fresh brake fluid. And by the way, use fresh brake fluid.
Make sure you don't switch the calipers, there normally is a "left and right" to them. If you switch them, you'll typically end up with the bleeder screws on the bottom, and you won't be able to get the air out of them.
If you're hoses don't have a thru-bolt, make sure to screw the hoses into the caliper before you mount them. Reversing this procedure doesn't work. :)
If your hoses do have a through bolt, normally there is a copper washer for each side. Don't lose these.
When you have the calipers off, you'll lose some brake fluid. (This is good, you really want to flush it anyway.) Do make sure the lid is on the master cylinder, though, or you'll end up with air in the master cylinder and that's a hassle.
Once you've reassembled everything, you can usually do most of the flushing and refilling and bleeding quite easily. Top off the master cylinder with fresh fluid, and then open the bleeder screws on the calipers. Normally over a few minutes the calipers will fill with fluid and start dripping. Make sure you don't let the master cylinder go dry or you'll get air in it. Once the calipers are flowing clear fluid close the bleeder screws. Gently pump the brakes up so your calipers are gripping the rotors. Then rap on the calipers a few times and re-open the bleeder screws. If you do this cycle a few times you can usually get most (if not all) of the air out of them.