How much to spend per day??

I have just started a mobile phone review blog. I want to promote the site with PPC and can’t decide on the best spend strategy i.e. how much to pay as a max per click.
I worked for a company that spent £30k to £40k each year on ppc and only recorded around 90,000 visits for their money, their product was sold directly and the £3k they spent each month gained about £20k in sales. As a site earning money from affiliate advertising I estimating a 3% (if i’m lucky) return on visitors who click through and buy. So what would a realistic ad campaign budget be??
I’m not looking to make a fortune just enough to live!

See original post by nicsonian