There are so many websites and of course, most cost money to join.

Here's a https://www.irs.gov/businesses/cost-segregation-audit-technique-guide-chapter-4-principal-elements-of-a-quality-cost-segregation-study-and-report to the IRS website noting specific items that are included in the cost segregation study report. hmm, that website is a 404 error.  

Even a single family builds can vary significantly based on site conditions and required structure/design.

For example, to get up-to-date property tax data you would need to scrape every county's tax data website (thousands of different websites, data formats, issues, etc...) then aggregate and clean the data.

These softwares have a lot of functionality, but honestly there is a steep learning curve and the functionality is probably overkill for most rehabbers.FlipperForce - Web-based House Flipping Software built specifically for flipping & rehabbing houses w/ Estimating, Gantt Scheduling, Task Management & Budget ManagementGeneric Project Management SoftwaresThere are nearly an infinite amount of potential generic Project Management softwares available that provide powerful functionality for managing project schedules, tasks & documents. 

Quote from @Chris Lo: Which platforms/websites do landlords use to find the rent rate, how long the rental properties have been on the market, and all the details about other rental properties?

I was unmotivated when I posted this and was blaming it on the site, but it was how I was interacting with the site, not the site.

There are a lot of websites that offer the course online, or if you have a college near you, they also typically offer a class that satisfies the pre-licensing requirement.

.: I set up LLC's on the secretary of state website for $50 and it takes about 10 minutes. 

I recently signed up for BP and found the calculators on this site to be very helpful.