(Supply is also going up, but not fast enough to stop the rate of rental increase.)

However, this option also requires that they share their candy with other children who knock on the door and they will soon discover a rapidly diminishing supply of sugary sweets in their bucket.

If a contractor starts to do good work at a decent price eventually they likely will be flooded with business and up prices (supply and demand).Read J Scott's book on here from 123flip  

You will also have cleaning supplies, legal / accounting fees, and if in your area possibly AC maintenance.

Do you usually supply trash cans?

Still one of the lowest ranking cities for supply delivery.

Especially on the farm when I need to cut some metal away from a power supply which is 80% of the time.

Go to Home Depot and Lowes and ACE and hang out in the building supplies section, those generally are people who are contractors who know rehabbers or are rehabbers themselves.

You can do a square footage estimate - but that is only an estimate, and probably not a very accurate one until you've got a bunch of experience under your belt.You can line item all the "stuff" - this takes a very long time when you're getting started, and it's probably not very accurate either, especially when you are pricing at the HD, but a lot materials are going to come from a contractors supply (if using licensed contractors), and labor rates vary greatly.You can try to get a GC to come out and give you an idea of cost - but be aware that GC's don't like this, especially when they show up and find "another cheapskate investor trying to slap lipstick on a pig". 

I also pay less for electric, water, sewer, gas and supplies.