When choosing a Delhi SEO company, you need to have established your exact requirements so you can monitor their performance accordingly. There is no point in hiring an SEO company and continuing to pay them monthly and yet not getting any results from the work that they do.
There are several Delhi based freelance seo expert companies that you will find online, each of them having varying levels of expertise in the field of SEO and digital marketing as a whole. Some of them would have flexible packages so anyone with any budget level could benefit from while others would tend to be expensive as their services may be geared towards companies with huge marketing budgets.
You will therefore have to decide which company you would like to hire depending upon your budget but always monitor their activities and seek weekly updates on what is done to promote your website. SEO is not a quick thing as it takes a while to see results but only when things are done right.
If you hire the wrong company then you will never see light at the end of the tunnel. You should be going through Google webmaster guidelines to ensure your SEO company does not violate their terms as that could result in a penalty for your website.