An investor who accepted to help me get started, asked me to put up the money for the repair on a property that is already purchased (I am not on the deed or title) for a return of 50% of the money I put in (after the property is repaired and sold) and When I asked, what's my security on the money I pay, I was told that we will be signing an affidavit of interest in real property.

It appears you have low percentages for vacancy, CapEx, and repairs.

I need a storage option so I have these materials for when tenants move out and I need to make repairs.

Sense I was 14 I’ve wanted to flip houses, I’ve worked in carpentry, painting, I can do minor electrical and plumbing, I’m currently working 2 jobs one in HVAC and one in chimney sweeping and chimney repair.

Your repair costs seem like they may be accurate but the other factors are the problem here, this is expensive for what you get in TX and I'm going to assume that it is in the downtown of a major metro area which is why the price is so high.

for a flipper the numbers may be tight using the 65% ARV - minus repairs math. 

The condition of the kitchen and bathrooms, outside concrete work and the condition of a possible front porch, exterior brick or siding repairs, is the exterior landscaping OK, closet space, any drywall repairs or painting.

Be sure to set aside money for vacancies and repairs either way when you calculate your cash flow.  

My reading and a fellow investor taught me that it starts with understanding the 70% Rule which is a quick rule of thumb that can be used to quickly analyze a rehab deal or wholesale deal by applying a 30% discount to the ARV (less repairs).70% Rule FormulaQuick analysis assumes profit and fixed cost will make up 30% of ARV(ARV * 70%) - Repairs = Rehabber’s MPPDetailed analysis breaks the 15% into a detailed itemized list...ARV - Repairs - Purchase Costs - Holding Costs - Selling Costs - Profit = Rehabber’s MPPThen, in order to determine Wholesalers Maximum Allowable Offer you would use the following formula:MAO = Rehabber's MPP - Wholesale ProfitWhat I need to be able to do is use the Max Purchase Price formula (detailed analysis) in order to calculate a more accurate MPP.

That does not mean you just simply pay less, it will have effect on your entire investment (longer commutes to check on things, lets buyers / renters, more days on market, lower rents, lower appreciation, etc).You will still need about 30-50k in cash to make this happen (20-25% down, repairs, closing cost and other expenses so keep that in mind.You also said "cashflow from day 1".