That's not such bad news. the Cascade's a nice-looking and stout little boat, and the electrolysis is the price one pays for 10-year old zincs. Expensive, but if that's the only major problem, then not bad for a long-neglected boat. They don't have much exterior wood trim, which is not as beautiful but good for non-maintenance and keeping your repair bills down.
Listen to your surveyor and be guided accordingly. These boats, in good condition, seem to list in the $30-40K range. So you can spend a little money and it'd probably be worth it.
Just some general advice: if you're going 60 miles offshore to bring her home, and the main's indeed shot, borrow a mainsail from someone, even if a bit undersized. It's not a good idea to make a passage on engine alone, you want to have at least a main of some size (preferably reefable) and a working jib as a backup--if you need them, you'll really appreciate it, and the sails will make the motion in a sea much nicer even if you're primarily motoring. It goes without saying that you'll also want the typical safety gear (firefighting, lifesaving) and good anchor and rode, and a VHF radio.
Apologize if I'm telling you what you already know.