Add on another $100 per window to have my contractor install them, and at absolute worse, I'm around $250 per window. 

He said he was going with the other offer and I was alright cause I have 4 other rehabs going on...pretty substantial ones as well and this house would be a big one as well as I'd have to add on about 1000 sq feet.

I'm just a little upset about the numbers they gave me, it seems that in this case, they didn't go there to get a clear picture of the conditions of the house and that they estimate the ARV comparing this house with properties that have higher sqft and had other add-ons.

How can I maximize my revenue with other add-ons (low capital of course)?

You have to use a QI so it's not an add on. 

@Daniel SpaizmanTo add-on to @Michael Seeker response:conventional residential loans tend to have less variety in loan parameters.

It may sound nice to pay a 5% management fee but the extra fees can add up to be more than the other company that charges 10% with no add-on fees.

It may sound nice to pay a 5% management fee but the extra fees can add up to be more than the other company that charges 10% with no add-on fees.

I actually forgot to add one vital piece of information.....right now I am positive cash flowing $450 a month.

Try to put a add on Craigslist for someone to take pictures of the property's you are looking at.