def strategy_cheap(cookies, cps, history, time_left, build_info):
    """
    Always buy the cheapest item you can afford in the time left.
    """
    items = build_info.build_items()
    costs = {}

    for item in items:
        cost = build_info.get_cost(item)
        costs[cost] = item

    cheapest = min(costs)
    if cheapest > cps * time_left:
        return None

    return costs[cheapest]