Let's start with the more straightforward system which was established in 1858. After this date the State took over the administration of wills in England and Wales from the Church. All wills have since been proved at the Principal or District Probate Registries. These wills have been indexed by year alphabetically and these indexes are available to view at the Principal Registry, London. They are also available to view on microfiche at some other UK Record Offices. These indexes are very easy to search, they contain a summary of the will which often includes very useful genealogical information.
Take this example- 1884 Timms, Gregory 5 May. The will of Gregory Timms late of Rose Cottage, High St, Dover, Kent ... bootmaker who died 7 Jan 1884 at Rose Cottage was proved at the Principal Registry by John Timms of 124, Briargate, Dover ... Schoolmaster, the Son of the sole execrutix. Effects, £94.
The full copy of the will can then be ordered from the Principal Registry in person or for postal applications - Probate Searches and Copies Dept,Duncombe Place, York. For more information on how to do this see http://www.courtservice.gov.uk/fandl/prob_guidance.htm. Alternatively an agent will do this for you just as cheaply.
Before 1858 searching for wills is more complex. Probate was granted by The Church of England and wills were proved in a variety of Eclesiastical Courts - Archdeacon`s courts, Consistory Courts, Commissionary Courts, Prerogative Courts of Canterbury and York and lastly strangely named Peculiar Courts. Different geographical areas tended to use a particular Court although not exclusively so. Fortunately to simplify matters most wills before 1858 have now been indexed and both indexes and wills can be found in the County Record Office concerned.
For a list of County Record Offices see - http://www.oz.net/~markhow/englishros.htm. Record offices are usually very helpful and will respond to written enquiries. Most are now on e mail. You could enquire whether they have a reference to your Ancestors will and if so the cost of photocopying and postage. Prices will vary, but will probably be around $1.00 USD ($1.50 CAN) per page plus postage. They may also make a charge for their time. If you use an agent they will be able to do this for you just as cheaply.
Philip Westwood runs a genealogical service enabling Americans and Canadians to research their English Ancestors. For more details view his profile.