FYI: Last time I stopped at the bank where I opened business checking account 2+ years ago (Wells Fargo), they sat me down and offered a 100K line of credit (the interest rate was unknown unless I applied, but she said it would be around 7-8%). The service is poorly monetized ( disproportionately high hosting fees + new hardware expenses / revenue). Until recently I was putting all these hosting related expenses on a single US Bank credit card (and paying it off monthly). In response, they raised the credit line to 40k at 8% yearly interest. This is less however than the 300k, that I think is needed. Additionally, I would prefer to use this kind bank debt financing only in an emergency, because I suppose that unlike a savvy investor, Wells Fargo and US Bank would be absolutely inflexible if I say need slightly more time, and would drive the company into default by their blanket policy, regardless of the specific circumstances.

Not unless you're willing to put up (say) your house against it. If I were a bank I wouldn't be willing to take the risk that your business will go under before it ever pays back the $300K.

Basically you need a small-scale VC or large-scale angel investment... or else to continue to bootstrap.