They are probably harder to do CORRECTLY than a new topend...
I rebuilt BRRACUDA's rear caliper and it was a beyatch. Took about 4 hours including sandblasting which was mostly done to get the parking brake free but he blocked it off anyhow. The slide pins seize, the pistons won't come out; Over the years I have found ways to deal with them without destroying them.
Apparently there are some year CR250 or 500R front calipers that have plastic pistons that work great. The stock pistons if they aren't too bad and no one put Channel Locks or Vice Grips on them, can be cleaned up in a lathe with WD-40 and some 600 grit emery cloth.
I can rebuild calipers like new but each one needs different parts to repair them.... The parts aren't very expensive, that labor can add up but I was very fair to Paul and always fair to everyone, I don't watch the clock......
All our government does is distract us while they steal from us, misspend our tax $ and ruin our country