It depends on how old school it is. If you have an old 70's Squareback Redline or the sort, it could be worth quite a bit depending on the condition it's in. Other individual models are valuable as well, but most aren't worth even half of what they cost new. It depends on the bike.
Hit eBay and Craigslist to find out what similar bikes are selling for.
redline
No the x10's are currently not sold don't ask me why that's just what my research has shown
Yes
Redline has been in business for quite a while and have produced solid bikes. While not an "upper-tier" company, they're a great company for a first BMX bike.
1996
Dk, Redline, PK Ripper, Diamond back, Haro
Mostly in China, although their ultra high end pro BMX bikes are made here by private frame builders.
ANSWER: I believe that Haro is the best BMX complete bikes for the money. I love my Haro BMX race bike.
Linn Kastan and Mike Konle started Redline in 1970. Originally they built Motorcycle frames. In 1974 Linn built his son a BMX frame for his son's birthday and that's where it all started. In 1988 Linn Kastan sold Redline to Seattle Bicycle Supply and started Kastan Bicycles. Linn Kastan also invented the tubular chromoly fork.
i recomend a dimond back or redline but dimoned back is cheeper!
Redman BMX frames are very good, but overpriced.
The lightest bike for adults is probably a redline or a hyper but hypers are kind of expensive