I know you want a dollar amount but that depends on the market you are in and the class of property you are working on.To give you a perspective that you can relate to, a factory worker with a moderate skill level as say a machine operator will earn $10/hr.

Sometimes its all capped out and overvalued and sometimes there are huge opportunities for growth that are not being utilized such as adding a laundry facility, vending machines, garage parking, storage etc etc etc. 

I purchased a property cash then did a delayed financing loan shortly after. https://www.therealestatecpa.com/2016/05/22/ultimate-guide-irs-schedule-e/ Reading through @Brandon Hall's article and the IRS publications it seems some items go to adding to the property cost basis and get depreciated, others apply to loan cost basis and are amortized over the duration of the loan.

I say she has lived there for 2 years. 10 minutes later Jane doe calls me screaming that I'm going to kill her son who has an asthma breathing machine and she doesn't have electricity to use.

There is nothing quite like the sound of heels hitting the deck in unison and bodies moving as if they were part of the same machine.

Come home with a few addresses and jump on the old Google machine to find the owner.

Used machines are cheap.

I had a plumber run plumbing for a washing machine. 

Upon move in, she had a 3 page list of requests.These included new:New vacuum cleaner bags for a vacuum which was already in the house.A wooden strip added to the front door as she thought the gap was too wide.New electrical outlets for the whole house as the existing ones were old.There were some valid requests which I fixed straight away (AC wasn't cooling below 80, one electric outlet wasn't working, washing machine wasn't hooked up properly).When August rent was due, she paid on the 11th and gave me a doctors certificate and said to please forget the late fee.The lease calls for a $75 late fee after the 5th plus $10 per day for every day it's late.

Tenants can be hard on common area laundry's so getting commercial, coin operated machines would be a better route to go.