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.
You need to spend A LOT of money if you try paid marketing. For example, Adwords is very expensive for hosting related keywords.
Try some free ways first, work a lot on this, see what results you get. Work for a few months this way, get some clients, work out any problems with your platform, your billing, etc, and then try some paid marketing.
Paid is also expensive when starting up you might need to start free. When revenue comes in dedicate some to paid so that you tap into another market you may not have. Its the best of both not ditching one for the other.
After having your website running, you need to promote your site in order to get traffic and revenue also. There're many ways to promote, for both free methods and paid methods.
Free methods such as: Doing SEO strategies, Social Media Content sharing, Youtube Sharing, Facebook Content, Twitter, Google+, Pinterest,...and many other channels that give you free using and promotions
Paid methods such as: Doing SEM such as Google Adwords, GDN, Solo ads, Facebook ads, banner ads,...
So it depends on your budgets that you will choose which methods that can give you the best effort, or you need to combine between free & paid methods in order to get the effective results