Replacing a caliper is a peice of cake even if your a novice. Just remove the line leading to it (have a empty coffee can handy to catch the fluid that will drain from it). Remove the 2 bolts that hold the caliper on and remove the caliper and pads. Install pads on new caliper and assemble in reverse order. Fill the M/C and open the bleeder on the caliper until fluid runs out. Tighten the bleeder. Have someone pump the brakes up and gently loosen the bleeder screw about a half a turn and tighten it right back up. (NOTE: wear saftey glasses when doing this, sometimes it will spit brake fluid at you). Try to do it fast enough so the brake pedal don't go to the floor. You may have to do the bleeding process 3-4 times to get all the air out. Make sure and don't ever let the M/C run dry on fluid or you'll be bleeding the whole system.
Sorry can't say what a total brake job will cost. That varies quite a bit from car to car and areas. You'd just have to get a quote from your local shop.
Brakes are of course one very important saftey item and if you don't feel comfortable working on them your best off getting it done professionally.
BTW: Is the fluid for sure coming from a caliper? Could also be coming from a line or the copper sealing washers that seal the line to the caliper.
