Mind you, its not ancient (1996 I think), but it definitely needs some work. (TLDR at bottom)
The bike in question is a Huffy Blackwater that I got for my 12th birthday, rode it constantly until probably 16, then it sat for 2 years in my mom's garage (hanging from the roof actually). My brother helped me clean it back up (new chain, re-lube everything, knock the rust off the gears, etc) and it rode nicely. Went off to college, but never had a way to bring the bike, so it stayed behind. Came home at one point and the gear lever is broken (can't change out of high gear) and returned it to the rack.
Finally, 5 years later, I'm back in town, and I pull the bike off the rack, fill it full of air, and give it a test ride around the block (in high gear mind you). The back wheel is a LITTLE wobbly and I only feel it when I brake, front brake works fine but is inclined to stay cock-eyed and thus one pad is rubbing (have to twist the caliper so it doesn't), and now it seems the rear gears have also locked up (can't change out of 3rd on the rear wheel).
What is the cost to get a wheel re-aligned or would I be better off buying a new one? Whats the best place to purchase replacement levers (shifters?) and the mechanism that changes gears (derailleur?)? The lever says "Shimano SIS" and its a 3x6 (18-speed). I don't really have the money for a new bike, so I was hoping to fix these minor issues and ride this one for a while. The bike has a little rust at the handlebars (the hex head) that I was going to remove and inspect, but otherwise, it seems very sturdy and no visible rust (or paint bubbling).
TLDR; pulled out 15 year old bike (Huffy blackwater), no rust, stuck in gear, wobbly wheel, broken gear lever. Best place for parts; new wheel or re-alignment?