If you want cheap and light, go with a Savage and Barska Swat scope. You can get it .223 with a sporter stock for under $500 and the scope for under $300. There was an article in SOF about 2 or 3 months ago about that rifle. I have a Savage with a McMillan Stock so does not even come close to your weight specs. Jensen Arms had a lot of the sporter stock in stock last time I was there.

http://savagearms.com/10fp.htm