The week my budget spreadsheet saved me from a $400 mistake

Last Tuesday I almost signed a lease for a place on Lyons Ave that was $150 over my cap, but I had this running cost chart in a notebook (yes, physical paper, I'm old like that) and when I added in the extra utility estimates that the landlord glossed over, the total jumped to $1,450 a month. My gut said the place was cute, but that number screamed no. I walked away and found a studio two blocks over for $1,250 with water included, which is basically a unicorn in SCV right now. The funny part? The landlord called me three days later offering $100 off because nobody else bit, and I almost said yes out of guilt. Has anyone else had a near miss where a simple list on paper saved them from a fancy apartment trap? What's your cutoff line between 'worth it' and 'run'? I need to know I'm not being too strict with my numbers.