It isn't a question of how much you spend on advertising, it is the question of HOW you do it. You can find brilliant methods that maximize return that are either free for you or cost next to nothing, or you can spend thousands of dollars and not convert at all.
Before anything, the key questions is to identify who your client is (who are you going after as first order of priority) and how much money do you have, if any, to reach that clientele. Then create a mixture of both - free and paid ads.
For example, if your answer is your local businesses, then participating in local/community entrepreneurial meet-ups likely won't cost you anything. Reaching the same businesses via direct mailing or local newspapers will. Both reach the same audience, except one of them requires money and more time.