One of the challenges to interpreting prices that show up in historical texts is that the coins listed, and their equivalent values, are unfamiliar to most modern readers. British currency shifted into its current decimal system in 1971. Prior to that point, its major currency values were in terms of pounds, shillings, and pennies (pence). These are often abbreviated as £ (l.), s., and d., from the Latin, librae, soldii, and denarii. There are 12 pennies in a shilling; and 20 shillings in a pound.

Prices are often written in £/s/d format i.e., £5, 10 shillings. 6 pence, or 5/10/6. If you see an amount referred to as "ten and six," it's safe to assume that it means 10 shillings, 6 pence, not 10 pounds, 6 shillings.

Because of fluctuations in the availability of gold and silver, a variety of coins were minted during the 17th and 18th centuries, and you may see prices referred to by the names for specific coins, rather than in £/s/d. 

Farthing: 1/4 penny

Halfpenny: 1/2 penny

Half a crown: 2 shillings 6 pence

Crown: 5 shillings

Sovereign: 20 shillings (1 pound)

Guinea: 21 shillings

Fluctuations meant that the value of these coins could change: pound coins shifted slightly, but the value of the guinea tended to rise sharply and decline again until its value was fixed at 21 shillings in 1816. In order to avoid confusion, some British merchants listed prices strictly in shillings and pence, i.e. "31 shillings 6 pence" instead of "1 pound 11 shilings 6 pence."