We got hit with some surprise costs that I can’t afford.

You say she can barely afford your rent but now she’s paying that rent and presumably rent at another place she’s staying?  

It's because agents aren't understanding affordability is constrained.

When looking for options for something pre-fab to plop on our lot, we keep seeing things about Amazon homes and they seem super affordable, but I don't see a ton of information on them and how to plan for the house arriving.

I can afford the loss.

Long-term investment should cover income shortfalls and consider alternative markets outside San Francisco or affordable markets like Texas, Ohio, or Arizona.

Start with a single family home at areas where I could afford and have a stable cashflow    Pros: Easier to manage    Cons: Would have no equity to invest in my second propertySome background about myself:Have a full-time job ($190K a year income).

For stable markets, consider places in the Midwest or Southeast where properties are more affordable and rental demand is strong.

Basically you can afford -3500/month which equates to ~$500k if no rental income.  

Someone here said don’t invest anything you can’t afford to lose and that is our approach but we are bullish on cypto currency right now.