You would be better served to collect quotes from a handful of foundation specialists then choose one.As for costs, it will be dependant on many factors: type of foundation; type of soil/rock; depth of underpinning / ease of soil removal; and your location.

I actually bid up the price between myself and the auto bid software to what I felt was the rock bottom lowest they would accept, and they did!

If you're putting up 100% of the capital and they have no skin in the game that's a red flag to me.

You're starting off in the red, your only option to be the least in the red is to raise rents as much as possible as fast as possible.Using your numbers and some other assumptions such as starting at 900/mo rent I get a 7.24% IRR.  

That being said come August/September landlords facing vacancy are forced in between a rock and a hard place.

I think your strategy is still rock solid.

@Michael Vallee, I wouldn't have any trouble getting that loan financed as a broker if no red flags popped up.

Sounds like you would have no control... first red flag

Some will have a lot of kids who get out of the car drinking red pop and eating chips.

Don't invest in Europe.It doesn't work like in the US.Prices are way too high, rents too low, they will tax you to death on rental income(Portugal is 28%, Germany is 40%) and there is red tape from here to Mars.