When taking a Cherbourg ferry from the UK there are three ports that you can sail from, specifically Portsmouth and Poole in England or Rosslare in Ireland. There are also several different ferry providers that you can sail with.
If you sail from Portsmouth to Cherbourg you have the option of booking with Brittany Ferries or Condor Ferries. The Brittany Ferries service is the faster of the two, taking just 3 hours on average, while the Condor ferry takes around 5 hours. Condor also only sail one ferry a week from Portsmouth while Brittany sail eleven and the Condor service only runs in the summer months. A return trip with Brittany Ferries starts at around £62, there are currently no prices available for Condor ferries, but expect them to be fairly similar.
Going from Poole to Cherbourg gives you no choice but to travel with Brittany Ferries. They run both fast and slow ferries, and on the fast one it's a crossing of just two and a half hours, however the slow ferry can take substantially longer. Prices for a return ticket start at around £50 and they run 15 ferries a week.
If you are travelling from Rosslare you have the choice of either Celtic Link or Irish Ferries. They each only run three ferries a week, and it's a long crossing of at least sixteen hours. However whichever operator you travel with prices start at around £60 for a single foot passenger buying a return ticket with no cabin or extras.