Flipping (or wholesaling, brokering, developing, or managing property) isn't passive. Those are all active jobs, though very much real estate related jobs.
$40K isn't enough, as far as I can tell, to seriously get into commercial. Some of the NNN type commercial properties seem to generate some decent returns, but it seems like you need a million bucks or so to get into a property like that.
I'm not quite sure how to interprete your budget statements. Do you mean you need to come up with an additional $700 a month to make ends meet? Or, that you only need $700 a month out of your $130-150 day job income and have the rest of it left for investment?
If its the former, then you may want to take a run at one of those RE jobs. They take work, but you seem to have the time. Fix and flips should generate 10-15% of the selling price as (fully taxable) profit. If you target $100-200K houses, you would only need to do a few a year to make up that $700. But it will be a job.
SFRs or small multi-s seem up your alley, if its the latter. If you're only using $700 a month out of a $130K a year paycheck, you would have $5000 or more a month to invest. From what people have written here, its entirely possible to find good deals in Houston. Read in the Rental Property forum about the realities of rentals, if you haven't already. You don't have big heating bills there (I lived in Houston in the 80's and 90's), but you have ACs to run and maintain, termites to eat your houses, and killer property taxes. But I think you can find good deals that will have true cash flow even after accounting for the 50% rule. I find bunches of 3BR houses on the MLS under $50K and rentometer says rents of $1000 are on the low side. So, just that very quick and crude check says good deals are possible. With W2 income your borrowing situation is much easier than for someone who's trying to be a self employed landlord. With $40K in cash you have enough for down payments and fix up expenses. Creative techniques like owner financing would help you conserve your cash. If you have $5K a month coming into this process you could accumulate quite a few properties quickly, provided you can get financing. Develop a good relationship with the decision maker at a smaller bank or two. Buying small multis (duplexes, quads) will let you accumulate more units with fewer loans. As you accumulate properties, look at ratcheting up by selling the individual ones and 1031'ing into smaller apartments.
Jon