One tender came back well above the others and we discounted it
Sometimes that gap is greed. More often it is the one firm that knows something about this job the rest don't.
What's happening?
The instinct with an outlier is to bin it and move on - three prices agree, one doesn't, majority wins. But tender prices are not votes. The high number is often the firm that has done this exact work before: the one that knows the ground is wet, the access is worse than the drawings admit, or the specification item everyone else skimmed is expensive.
The cheap cluster can simply share the same miss. One conversation settles it: ask the outlier what is in their number that isn't in the others. Either they name the thing - and you have just learned the job's real risk for free - or they can't, and you discount them with a reason instead of a reflex. Tender analysis builds that question in, so the decision gets recorded rather than made on instinct.
The solution
Find out what the expensive one knows before you bin it.