I'd suggest looking at either a hardtail mountain bike instead of a full suspension bike. You'll get a lot more bike if you get a hardtail.
I may have a bias since I'm a roadie but I do own an aluminium hybrid and they are very good value for the money. You should check with any local bike shops (in person) and see what they have in 2010 models in your size. You can get some really good deals that way.
The other thing is be prepared to spend a little more than $300 if you want to find a bike that you can get easily serviced and repaired. If you break a store brand bike say a year or two from now then you'll either be waiting for weeks for a part to appear or you'll be out $300 because it can't get fixed. The other thing is that their resale value is nothing. A quality bike from a well known manufacturer will also allow you to upgrade the bike as well as have some resale value.
I'm assuming that you're an average size and weight so there shouldn't be any issues there.
You also didn't mention what area you live in or where you were planning on buying. I've always dealt with local bike shops instead of ordering by mail or by internet for simple reason that your LBS will find you a bike that will fit you
as well as something that will suit your budget and needs. It might cost you a few more bucks but it can save you a whole lot of pain. They also can sell you a package where they can sell you stuff like water bottle cages, water bottles, bike shoes, a good lock, repair and tool kits etc.. with a 10-15% discount.
Any entry level bike in the 300-600 price range will most likely have a steel frame and will be tough durable and heavy. If I were carrying stuff around, I'd go for the lighter bike.
I see that Norco has offerings in the $300-400 price range
steel frame at $324 but it's a 2010 you might not be able to find one.
aluminium frame at $360
Giant and Trek also make similar bikes (all hybrid) in the $300-400 price range.
I've got three sons, two of who are in university and we got all three of them some entry level mountain bikes (Norco, Trek) about 4-5 years ago. Parts and service has never been an issue.