If you are going to buy links the first thing you have to do is to find out what the link looks like
. You have to discover the quality of the link. The quality can be based on relevance and other forms of measurement. I would suggest you avoiding site-wide links as in many cases they cost much and give little value.
Quite a lot of people are worried about their rankings in search engines and try to find out whether it will harm their ranking if they buy links or not. To tell the truth there is no certain answer to this question as all depends on the reason of buying links. For example, if you want to buy links to evolve more traffic to the site or for publicity then the quality of the link is not so important for you as in this case you will be concerned about finding sites where there are quite a lot of visitors. But if your aim is to reach high ranking on the search engines then you should be very careful to buy links from the right sites. If you buy links from the wrong sites by mistake then you will get into trouble and will need to do tremendous work to clean it up. And as a result of your mistake of buying the links from the wrong places you will waste your money and will spend much time to retain the love from search engines. In most cases you will not even be able to do it.
Besides, if you are not going to spend a lot of money monthly it would be better if you find cheaper links. In the internet you can come across a number of sites that promise hundreds and thousands of links but later you'll find out that many of them are just junk. If you are looking for quality links you should better not to look for sites that are hosted on the same server, company or IP address, or have the same or similar content. This will not be good for you and can make you trouble again.
If you want to buy links I would like to suggest you buying such links as for example Conferences. If you pay to attend a conference and are sociable there would be some people who probably will reference you on their own blogs.
Another link that will also be good for you is Testimonials. Testimonials are considered to be a sign of social trust and consequently can help you to increase sales.
Awards is also a good link to refer to. Since people like recognition, winners like talking about their achievements. You can even gift the winners some of your products to make them talk about them.
Another link that I would suggest you to pay attention is Donations. You can support causes that you believe in and donate money for them. In some cases you will also be able to donate software or other services that will not cost you much.