Look man, my uncle's a structural engineer and he'd lose his mind reading this. That $4500 quote probably wasn't just for patching a crack. They were likely quoting for what they could see from the inside which is never the full story. Hydraulic cement is great for stopping water in a pinch but it doesn't fix whatever caused the crack in the first place. Settling soil, hydrostatic pressure against the wall, bad drainage outside - the crack is a symptom not the problem. I've seen guys slap cement on a crack only to have it fail six months later when the ground shifts again and opens up a new one six inches away. You might be dry now but I wouldnt call it fixed.

Oh man, I feel your pain on a deep level. My best friend told me she spent a whole morning trying to get her kid's construction paper snowflake to stay up, and it kept curling at the edges. She ended up using washi tape, the kind that's a little stretchy, and then a few of those clear pushpins she had lying around. That snowflake stayed flat for like two weeks until it got replaced by a crayon drawing of a weird-looking dog. It's a whole system, you know?