I can't tell the specific model, but I can tell you a little about the company...
Giant is a well respected company, and in addition to making their own bikes, also manufactures bikes for many other bike companies, going as far back as making some of the imported Schwinns back when people names Schwinn still ran the Schwinn company.
If a certain company doesn't manufacture their own bikes, there is a chance that Giant might. They are one of the largest manufacturers of bicycles in the world.
As far as the specific bike, if it is 100% ready to ride with newish tires/cables etc and no signs of significant wear to any components, depending on where you live (since vintage bike value is impacted a lot by where you live) it could be worth up to $250-$300. Deduct for anything that is less than new looking and ready to ride... Also deduct some if you are not in a market that is really high cost in the used bike market.