Bids for a renovation and expansion project at Central Bucks East High School have come in well below earlier estimates. The bids from six contractors total about $28 million, $7 million below the estimated cost. The plans call for upgrading classrooms, replacing the plumbing, wiring, heating and air conditioning systems and building a 30,000-square-foot addition to house a new Science and Technology Center. Construction should start next month on the addition, and the rest of the work should start in December. The whole project should be finished in about three years.