rwilson - 1:44 pm on Sep 18, 2012 (gmt 0)

So basically your saying you were going to link to someone's widget because you found it useful and before you could they offered to pay for a link.

It's against Google's guidelines for them to pay for links however, shouldn't affect you in any way, but in this case it seems like the content is very relevant to your site.

I would do it and maybe indicate you had your own write up in mind, it would seem like a more natural link and would benefit them more.