I cannot qualify for a portfolio loan as my DTI is above the requirements even though my credit score is >800 and I don't have 20%-30% to invest.

Low credit score, 500 something. little cash.

I meet one of the good houses tomorrow and I want to score this one for sure .

Here's one I found with a quick search : http://www.nerdwallet.com/blog/credit-score/building-credit/ This doesn't mention the share secured loan, but they do talk about secured credit cards, which is basically the same idea, only with a card account- you pay the money to the credit card company BEFORE you spend it.

Checks are incredibly insecure.If you are going to use checks, I suggest you write them with an Ink Gel pen made for check signing.

I know I would get auto loans and they would pull my credit score.

If someone has a low score because they've had problems with cable/cell phone companies, gym memberships, medical expenses etc. but have always paid rents I'd consider them.

Is it possible to get approved for such a low mortgage or will the points always be too high if credit scores are below 740?

A long shot too.So, had you been more reasonable in the offer in the first place and not caused a stink and drawn unwanted attention from the lender, an installment sale/subject to may have been a score, now, I'd probably walk away.That's the reality form experience, for newbie buyers, others may discuss delusional options, but I'd say you're probably done.  

In 2008 I had gone broke going to school out of state and getting a collection on my credit score, it suddenly became very difficult to get loans to go to school (keep in mind, I had no support from my parents and was living on my own).