From experience, IB usually offer promotional upgrades to Business on intra-European legs such as this one for EUR60 at online check-in, or at the counters.
I personally wouldn't see any advantage to making a bid at ~£56 if there was a chance at check-in that it would be less. I'd also be surprised if the Business cabin is particularly busy between Madrid and Lisbon when operated by a widebody aircraft, so I'd say you would have a decent chance the promotional upgrade would be available.
One thing to remember if you're chasing Tier Points or Avios, is that unlike BA's promotional upgrade offers, IB's only credit Avios and TPs for the original purchased fare, not the upgraded class of service.