You could need a valve, you could need a head, you could need an engine, or you could just need a new timing belt. I would not buy a timing belt or anything for it until you have it checked. I have heard of people breaking belts and nothing happening, and I have seen ones that resulted in major damage to valves and pistons. My b20 that I bought from a salvage yard had the corner of the valve cover smashed into the cam gear so that it pinched the belt (I bought it because it was the cheapest and had a warantee). When installing a timing belt before putting it in my car, I notice that there were teeth ripped off the timing belt and the crank was 180 degrees off. I pulled the head and inspected the valves and pistons and discovered absolutely no damage, so I put a new head gasket and new timing belt and it runs perfect. From personal experience, it is possible (at least on a B-series engine) to have a belt slip or break with no damage. Since your belt is broken, your crank is probably not lined up correctly with the cams, so you definitly have to know what you are doing just to get a timing belt on it without hitting valves when lining it back up (I didn't have any trouble because I had the head off and cams out). Anyway, definitely have it checked out before you waste any money. Were you driving or stopped when it broke?