There has been a lot of discussion on these rifles. If the gun is the older model the price you state is not all that great but is fair. The older models were selling quite cheap a few months ago as the big stores were moving old stock. If the rifle is the new S2 version then under $500 is a great price.
Vanguards are a solid well built and accurate rifle. Not too many complaints but some one will always have something to say. I've owned two and have no issues.
I currently have an S2 model in 7 08 and I wont be selling this one any time soon. It took a little playing around with loads but it shoots .75" with no problems now. It is solid feeling in the hands and does not have that cheap feel that other brands in this price range do. Also, the trigger of the new S2 is much better than the older model.