Given that you've put this in the SEO forum, I assume the reason you're asking about it is to improve your ranking in search engines rather than any other reason.
In which case, the answer is "don't bother".
Any links that you pay for must be marked as "nofollow", in which case search engines will ignore them and you will get nothing from them.
You've not mentioned what general topic or field you're looking for, which suggests you just want to indiscriminately spam every blog you can find. Spammers aren't nice people, you don't want to be one of them.
Google determines what a site is about (in part) by the context of the links pointing to it. If you have links from a wide and diverse range of subjects, from tropical fish to Alaskan farming methods to forums about the latest TV programme, Google isn't going to know what to make of your site, so you're unlikely to get any improvement in your rankings.
Even if you did go for a more targeted approach, it's still unlikely to have much impact. Most reputable blogs and forums (including Sitepoint) make all their outbound links "nofollow", precisely to discourage this kind of spamming, so you won't get any benefit from them. Most blogs and forums that don't make their links "nofollow" will either have so many million outbound links that you won't get more than an atom of goodness from the link, or they will be "bad neighbourhoods", and your site will be tainted by association.
A better strategy is to find websites that are relevant to yours, and ask for 'editorial' links to your site - ie, ones that can only be added by the webmaster/editor/author, and so there can be some level of trust that they are only adding worthwhile links.