I might suggest a mountain bike then, you can get ones made for the street for under 300 and they have multiple gears to make it easier if you live in a hilly area. But if you want a BMX i would look into diamondback. they are inexpensive yet, reliable for the use your looking for.
If you do take my mountain bike idea, look at schwinns, ralieghs or trek. they can be found for under 300 pretty easily just check your local bike shops.