So, you have optimized your promotion expenses and any increase is not bringing in new customers. This is natural. The bell curve is applicable in most situations and just increasing your Google Adwords budget may not necessarily mean an increase in the number of people visiting your site and buying your products. But you want more traffic and do not mind spending some money for it. So, what do you do now?
Have you considered offline promotion methods? True that your business may be essentially online but the people browsing your site and buying your products have a non-internet presence too! Have you ever tried to reach out to them when they are not connected to the internet? This is an area of promotion that falls into the blind spot of most webmasters. The simplest offline promotion would be business cards and classified advertisements.
It is considered customary to put your signature when you post on forums and someone not doing so is viewed as one who is losing some traffic everyday. So, it comes as a surprise to me as to why so many of us shy away from putting our business urls on our business cards. In fact, the business card will last longer than the forum threads on search engines and are potential business hooks whenever the need arises.
When it comes to classified advertisements, the usual reaction is "but then no one reads it". You could not be further from the truth. Offline classified advertisements are far more popular and read more than their online counterpart. Also it is possible to target the audience better with newspaper and magazine classifieds. Visit your local newspaper office and find out their readership volume. Assuming that even 5% of the people read the classifieds and I am sure you will start believing in a good return on investment. This is because of the low costs involved.
When you do decide to place a classified advertisement, try to keep the information as clear and as short as possible. This is critical and difficult since every word costs in the offline world. This is unlike the online classified sites where 100 words and above are very common. The next mistake that most classified advertisers do is to provide long and complicated urls. Remember that people cannot copy and paste from newspapers to their browser's address bar! Keep the urls simple and human readable. It should not be that difficult if you are able to use some redirecting software on your website.
Remember that online promotion expenses are more linear in that you keep spending regularly (everyday?) while in case of offline advertisements, the expenses come in spikes (weekly/monthly?). This usually gives the impression that offline advertisements are prohibitively expensive and is suitable only for large establishments. This may not be true if you can set your objectives of the campaign and keep track of what you are doing and how much you are spending.