Outsourcing content creation is a huge decision to make. You'll generally have the option of choosing between freelancers and agencies.
Both options can be great depending on your needs.
A freelancer is a self-employed writer who works for multiple clients at a time, while an agency has a more professional organized setup, with multiple employees and a wide array of clientele.
Pricing is more inconsistent among freelancers, but you will normally pay less for freelance services than an agency because of the lack of overhead.
On the other hand, freelancers can charge anywhere from very little to higher prices depending on experience and the extent of a project. A great freelance content marketer will often charge a minimum of around $100 an hour, but some who are the only ones capable of doing what they do may charge upwards of $300 an hour. The latter will be very familiar with the subject and may have connections to people in the industry who can help with promotion.
If you can't afford a top-tier freelancer who can write and market, you can still find ones who will charge less, but you may need another freelancer for promotion.
Naturally, agencies will cost more to hire because they offer a variety of services, with experts in content creation and promotion. They'll also likely have a team that includes a designer, writer, editor, and promoter.
Freelancers don't have to be at the highest level of experience or talent to work, as opposed to an agency. This makes it difficult to gauge the abilities of many freelancers prior to hiring them. You'll find terrible ones mixed with some of the best available.
Agencies can also be bad, but you're less likely to struggle finding a good agency, particularly if the agency has been in business for a long time.
Because you can get great quality work from both agencies and freelancers, the best way to find the right one is to look at past work and determine if they're right for you. Once you've found the ideal match, you'll be able to get the kind of results you want either way.