i just did it a week ago. really really easy.
hint of advice...
on mine. the actual mounting bolt for the wheel cylinder was rusted up bad. so instead of taking the old one off and risking breaking or stripping the bolt, i used the inside guts, and the outer rubber seals from the new one.... basically i rebuilt it while it was still mounted to the wheel.
very very easy.
i think the cylinder itself was 10 bucks.
just make sure you bleed the brakes on that side after your done.
just connect a tube to the bleeder on that brake, dip it down into a cup or jar or bottle of brake fluid. slowly pump the brakes. all the way down, all the way up.
this will push out any air, and pull back in fluid.
keep doing it until theres only fluid coming out with no little air bubbles.