Short answers, pulled from the story.
The Space Shuttle flew 135 missions between the 12th of April 1981, and the 21st of July 2011. Of those, 133 returned safely; two missions, STS-51-L (Challenger) in 1986 and STS-107 (Columbia) in 2003, ended in the loss of the vehicle and all crew members.
Challenger broke apart 73 seconds after launch on the 28th of January 1986, because an O-ring seal in the right solid rocket booster failed in cold temperatures. Hot combustion gases escaped and burned through the external tank, triggering a catastrophic sequence that killed all seven crew members. Engineers had warned NASA managers that O-rings were unreliable below 53 degrees Fahrenheit, but those warnings were ignored.
Columbia disintegrated during reentry on the 1st of February 2003, because foam insulation broke off the external tank during launch and damaged the carbon-carbon leading edge of the wing. NASA managers blocked requests for satellite imaging of the damage and refused a crew spacewalk to inspect it, so no rescue or repair options were evaluated before reentry. All seven crew members of STS-107 were killed.
Accounting for the entire program budget of an estimated $221 billion in 2012 dollars, the average cost per launch was $1.642 billion. From 1995 to 2002, when no new orbiters were under construction and there was no disaster recovery work, the per-launch cost was $806 million.
The Space Shuttle's retirement was announced in January 2004, and the final mission, STS-135, landed at Kennedy Space Center on the 21st of July 2011. The United States then relied on Russian Soyuz spacecraft to transport astronauts until the launch of the Crew Dragon Demo-2 mission on the 30th of May 2020.
Atlantis is on display at the Kennedy Space Center Visitor Complex in Florida, Discovery at the Steven F. Udvar-Hazy Center in Virginia, Endeavour at the California Science Center in Los Angeles, and Enterprise at the Intrepid Museum in New York.