Do they only work with realtors or do they also work with small scale investors?

Employees, subcontractors, vendors and suppliers.For a PM software and system you need a system like https://www.coconstruct.com/Or https://buildertrend.com/ these are critical to scaling the business.

The downside, it seems ,is that I may not to be able to scale as rapidly with new properties.

I used Cozy last year with my first unit, but am starting to scale up so I'm looking for something a little more advanced. 

Either small or large scale. 

I've done deals in 8 different states, but have been scaling back over the past year due to headaches and wanting to simplify my life. 

I'm not against cold calling, it's just that the skip tracing (using REI Skip), when done on a large scale, can have a lot of wrong numbers.

If you want to buy more than one rental, then you can scale faster w/ 30 year loans.In the world of real estate, cash flow and reserves are king. 

I believe they have the capacity to handle property management on a large scale like what you're looking for

As for correlating with purchase price, while of course there's a general correlation of higher price = nicer property = higher rent potential, it's not necessarily going to scale proportionately.