Rant: My coworker always insists on splitting the check evenly when she orders more

We have a team lunch every Friday, and one coworker always picks the most expensive items on the menu. Last time, she got a steak and drinks while I had a salad, but she still wants to divide the total by four. It ends up costing me double what I planned to spend. I tried suggesting separate bills, but she says it's easier to split evenly. Now I dread these lunches because it messes with my weekly food budget. I'm saving for a vacation, and these extra costs add up fast. I don't want to seem cheap, but it feels unfair. How do you handle split bills when someone spends way more than you?