Don't throw away hard earned cash when there are free means of testing pay per click. Sometimes it's handy to trial out an organic approach before spending months working on it. Others, it's just a matter of wanting to try and drive new buyers to the site. Amounts are in $USD, but are good to use in UK or elsewhere...
$25 in Bing / Yahoo advertising
$100 for Clients
$75 for Yourself
$50 Coupon for $5
Save 90%, though sometimes Facebook gives away $100 for nothing.