Recently I was in the same situation as you: a worn-out middle ring on a road triple. Although mine was on a Craigslist-purchased bike that was not nearly as in as bad shape as yours. Wow!

So a few seconds later I had a 9-speed Sora unit ordered on Chain Reaction for like $13. Works great. Steel, so adds a few grams, but the middle ring on triples always takes the brunt of drivetrain wear.