The thing is, a direct sales process that works & functions predictably can be more akin to a production cost then a long winded marketing cost. If you run a training/consulting business a 'course' could cost you $A to prospect & sell $B to host & $C to teach. As long as $A stays more or less predictable & A+B+C still allows you to cover overheads, it works. 'Affording' shouldn't theoretically be an issue.
The part that is akin to an investment that you can afford or not is creating a system where A is predictable & reasonable. That might be achievable with a 7k/month outsourced sales. It may be achievable some other way. What you need to invest in (time and/or money) is finding it. So, your first couple of 7ks are an investment. An experiment. If it works, affording should no longer be part of the consideration.
There are companies that basically are a sales process just like there are companies that essentially are a product or a technology. If you are going to be a company that is a sales process or a big part of you is a sales process, then you probably need to be directly involved.