Setting your PPC budget isn't a case of 'how long is a piece of string'.
Many companies shy away from spending large proportions of marketing budget on Adwords and other PPC Campaigns due to a lack of confidence within their existing campaigns. It sets about creating a catch-22 scenario - why put more money in when you can't justify the spend?
'How High Can Your Budget Go'?
The answer to this question is delivered by the success of your campaign. Companies who are managing highly successful PPC campaigns don't necessarily set an upper limit on their campaigns. They know that for ever £x spent there is a return of £y.
If you're struggling to find a route to increase your spend without compromising your marketing budget then it's time to talk. I work with a range of businesses who are sat in this very situation - they KNOW Adwords should be working for them, they either don't have the time or simply the patience in order to produce a sustainable campaign.
Why not have a chat about just where things may be going wrong and how we can work together to look at creating a remedy?