You’re… paying someone… to guest post… on their website? I… what?
They get free content… in fact, it’s not even free, you pay them to take your content, and you get a link in return? The newspapers are doing it the wrong way around, clearly…
This comes up time and again, so before anyone is misled and thinks it would be a good idea to post links here, let me make clear: most reputable forums (like this one) mark user-submitted links as nofollow. Link-dropping on forums is much more likely to get you banned than to improve your search engine ranking. It will certainly get you banned from SitePoint.
As to the other suggestions, any link you place yourself is regarded as largely worthless by search engines.
Create unique useful content that people would want to share and recommend.
Reach out to people who are interested in your content and have already linked to similar content. If it is quality content, they will be happy to link to it.
Look up the Skyscraper Technique.
As mentioned from other fellow contributors that most user generated links are nofollow, so why go through the trouble and waste your time doing that?