Doing SEO for your website is not always very expensive and difficult to do, especially if you have a very specific niche of yours and a website with solid age. Nowadays SEO strategy and tactics became very obvious, you have to make your website for your visitors if you want long term permanent results. From my experience i can say, that almost everything you do on your website and off your website for your visitors convenience etc. reflects on seo. Even new google's algorythm says the same thing, more attention is shown to good content, social sites, links from related sites etc. So doing real organic seo can be affordable and the results will be long term, ofcourse it takes time, but from my experience i can say that the longer i worked on specific keyword, the better results i achieved.

Cheap SEO tips:

1. Exchange backlinks with related content websites.

2. Make meta descriptions related with your website content.

3. Read and listen what google webmaster tool says to you.

4. Make your content really interesting and unique, and submit the best content to social sites.

5. Order directory submission services, they are usually very cheap, but worth the money.

6. Make sure your website navigation is convenient for the user.

7. Check your keywords popularity on google adwords keyword tool, to know which ones are worth optimizing.