i recommend Rebrandable Traffic site, they give you upon registering with them a free 100 credit for traffic of 100 people to your site.

That's how I got some of my refferals and when you spend that credit, ask a friend or relative to register on that site for free and send traffic to your site. That is how you can get paid traffic to your site for free in thousands.

a bit ago bing gave $50 free ad promotion I tried it out and it was quite good but I did not know enough to be effective in how I set it up. if you have not done some training might be worth doing some this might be of help An Introduction to PPC (Pay Per Click)

If you are advertising to get 'signups'; I read a recent article that $5 per day will get approximately 14 clicks and result in perhaps 4 or 5 signups....of those 4 or 5 signups, approximately 1 will purchase in future. As long as your site is drawig in the traffic to warrant the expenditure....go for it!

PPC advertising is a numbers game. Say you get two free sign ups for every 100 clicks to your ad. You may need around 20 free sign ups to convert one to premium (5%). That equates to 1000 clicks to your ad. At say $0.10 per click your cost is $100. You therefore need to keep your premium member for five months to break even and thereafter you are in profit. Obviously your ad content, your keywords and the landing page you send them to can have a huge impact on these figures and your conversions could be higher (or conversely lower).

What you can afford to start with, perhaps $5 a day I would suggest. Also, Facebook Ads can be cheaper and more effective than Adwords. Don't forget to add Adsense to your website to make a little money. :)

Best thing here is to follow Kyles training here: Setting Up Your First PPC Campaign

Kyle recommends to use bing ads before Google Adwords. Bing is more forgiving when it comes to affiliate links. I've just started with my campaigns so I can't help with budget.
One thing I do know is that when campaigning whatever your promoting the item should be worth quite a bit more than what your click costs you. One good thing about WA is the commission is monthly making your return from investment very good. Check out lesson 10 of 10 in the bootcamp. Hope this helps!