The best part about content (and inbound marketing) is how cost efficient it is.
Create the pieces yourself!
The pieces should be relevent to the email that you're sending. If it isn't then your database won't trust you and they won't open or click your emails.
Figure out relevant information that your customers and leads are looking for and start from there. One pagers, whitepapers, short videos, infographics, checklists, comparison charts...these things shouldn't take you too much time to create. They'll be relevant to your customers/potential customers, and drive interest in your brand.
Depending on your industry, sometimes it's worth it to have independent studies done, but that can still be big bucks. generally speaking, you should be creating content in house. Start with what your customers will find relevant and useful (note, this doesn't mean to spend time talking about how great you/your company is!) and brand your content/emails from there.
Good luck!
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