The figures don't make much $$ in cash flow using all the formulas, but my thought was to just keep renting it until I can get someone into a lease option to purchase.

Depending on what you plan to do with this property you have some room to play with. 190,000 *.7 = 133,000 - (Rehab, holding costs, and closing costs) = 75,000 (what your seller wants + tickets to see star wars)  Which means you have around 58,000 to play with for all of your unknown costs if you are sticking to a standard flip formula. 

I would also look at the lease rate formula to see how the lease amount will increase in the future.

I have purchased from the same wholesaler for the better part of 10 years and he has never deviated from this formula.

Banks generally use the formula that net rental income is 75% of the rent less PITI, which is a little more optimistic.

My formula is no secret.

Actually my cash flow formula is more complex and takes into account maintenance, vacancy, and a nicely padded misc/unexpected column for my own sanity and safety :) But I am glad you're making sure people aren't calculating it wrong!

Note that some of the formulas are not active.

His figures suggest there is a potential positive cash flow of hundreds of dollars a month, yet according to my back of the envelope calculation based on the various formulas I've learned, at those rents there would be potentially a negative cash flow of a couple hundred dollars a month based on 100% financing.According to his numbers, this seems like a great deal.

There are some formulas, but as a whole, you need to learn the art and can only do so by driving your areas, learning the market, walking lots of homes, and having access to real comps.