Costco has some but I think they are more then you want to spend. I'm pretty happy with my stack on from Academy that I bought for right around what you're wanting to spend.
Tractor Supply sells the Sentry G1055C for $299. It's supposed to be a 10-gun safe, but I don't see how that's possible with internal dimensions of 16x11 inches. It's got a combination lock (as opposed to electronic, which is also available), and weighs in at about 130 pounds. It's also not fire rated, but a fire-rated model of it is available.
I was able to pick up a Liberty safe for around $500 from costco.com a couple of years back. I've seen them for sale used periodically. I would check the usual suspects in online classifieds. They pop up now and again for the price range you are looking for.