Are you saying you screwed up the initial bid 5 years ago? Or the recent one right before work began? Because 5 years ago would absolutely not be valid anymore.

Any estimate I give has bold text at the end "Estimate valid for 30 days". Prices change constantly, products change constantly.
Systems I bid a few months ago may change price and feature set, customer has to get a new quote and outline of features after awhile. And if it is a large enough job that it takes me a few hours to re-quote, that is another design fee. Not my fault customer is indecisive, I'm not eating the cost of that.