It's kinda like a service fee... :)  Don't get me wrong, I own nice rentals in nice areas. 

Hey, what I have done In the past is provided my services to other investors where I partner with them and build the house and charge a management fee+ equity.

(Side Note: if you really want to jump your credit score in a few months (because it takes time for the reporting to update), and if your disciplined with your spending try this;1st) I went and did the math to see what my positive cash flow each month off my active income (let’s say you’ve got $500 left over after you go through your monthly spending avg. which is all you kick out vs what you bring in)2nd) Go get a credit card with 0% interest for 12mths with NO higher than 5% transfer fee.( their are some with low as a 0% transfer and I had got that one on my 2nd round cause my credit wouldn’t let me at first)3rd) do a transfer balance after 24- 48hrs of opening the card (Nope you don’t need wait to actually get the card just call in and tell them over the phone to send a Blanche transfer check to your bank account in the amount of your car Balance; because you’ve only got a 30day window of transfer with 0% interest for the 12mths)4th) PAY YOUR CAR OFF IN FULL, and take your old car note (let’s says it $450mth) plus your $500 positive cash each month and add all $950 each month to pay against the balance on the card5th) in 45days start checking your CreditKarma app (its free) and don’t worry about the 5% if it’s larger than your car loan % because once you’ve paid your car off your score will go up and in a couple months of $950 your car will be paid OFF not in 2more years or so...Thus saving you probably more than $2,000 in interest on the car loan (so you get to keep $$) and time in payments.Your saving money on interest (keeping it in your pocket thus making your pocket bigger!

Don't forget to get the deposit and any fees that might be owed

. $0 fee and zero remembering to do anything.

Is there variables that affect this fee amount?

I think it's okay for a mentoring fee, if you get LOTS of help and hand-holding and explanations from which you can learn.I think a 50/50 split may also an equitable way to pay for their help, but both is WAAAAYYYY too much to give up. 

The quandary I am in is that most of the money that the properties produce goes out the door to pay the expenses (mortgage, maintenance, capex, vacancy, insurance, PM fees, utilities, taxes etc).

If yes, you will have to cover monthly expenses such as mortgage payments, insurance, utilities, HOA fees, etc.  

If you want to build a business and develop a reputation as a “problem solver,” partner up with your seller... and if course save on fee’s and all the other jazz.