Since you're limited on a budget, you're limited to a used bike. You can definitely stop by a bike shop for advice, and they can show you what type of bike to look for. Typically, with your weight the main concern is the wheels. Make sure they are straight and true, and for frames its better to get one without shocks especially one in the rear. Do not get department store bikes, since they will not last long. Make sure the bike fits you and have the seat, handlebar, etc adjusted properly for your height.
Hope this helps.