I offered them 70% of estimated sales price minus repairs.

At the current appreciation (which I would have a local realtor run an actual CMA on as Zillow is typically 5-7% off) you have the potential to pocket nearly $100K after commissions and closing costs (I'm in CA and I typically estimate around 8% total commission/closing costs for my Sellers). 

I think it's the rental estimator tool here on BP. 

Your lender is required to give you an estimated number.For the sole purpose of dissecting comparables, I mainly look for different factors such as square footage, number of beds/baths, location, distance from subject property, etc.

While there may not be a large profit margin, there is not much to do to the property.Here are the details:Del City, OK Area (Oklahoma City, OK)1 Bed; 1 Bath840 Sq Ft on 0.38 AcreCentral Heat/AirWhole house pre-plumbedCount Assessed Value = $58,000Zillow's Estimated Value = $66,700The roof has a new deck, and it needs to be shingled, but he already has the shingles on site.

A GC can do a walkthrough and give you some rough estimates of repair costs.

Out of those sales you pay for product, overhead and split with the company building the store - they estimate profits of a couple thousand in a few months, around $5 to $7 in about 6 months to a year and more than that if you can built up higher credit.Names around the Amazon Store is Ben Fredricks (the guy from Noteworthy)Names around the Walmart Store is Mark Evens DM where the DM stands for deal maker.Any input around doing my homework on this type of investment or these particular companies would be highly appreciated.

Say you put $3500 down on a home for ~$120k how can I estimate the cash I need to keep in reserves for repairs?

No equity to compare.Cash outlay to hold is estimated at $40k. 

When you get a payment estimate for the hard money that should tell you if the deal is a fit for your cash position or lack thereof.