Alternative for Akismet - Comment Spam Pack?

I'm working with a client and looking for an alternative to akismet. There's no problem with paying for a premium product, but neither the client nor I want to deal with a monthly reoccurring charge. Since it is for a business and we aren't trying to abuse Akismet's policies, we would just like to find a pay once or annually option.

It looks like Comment Spam Pack might do it, but it seems like that is specifically designed for multi-site.

Any thoughts?

Thanks in advance.