i agree that you should get it roadworthy if you're inclined to do so. it's not a high percentage of people that have the know-how to bring a bike back from the dead. even among those that are capable, it's rare to find someone who does it just for the sake of getting more butts in saddles. it's a beautiful thing.

if for whatever reason you can't or don't want to fix it, it's perfectly okay to sell it cheap and tell the buyer that it needs some work before it's completely safe to ride. most people buying $30 bikes expect this.

cheers.

EDIT: if you do fix it, definitely sell it for more than 30 bucks. your motives may be pure, but your time's still worth something.