I stumbled across this resource today and thought I'd share it with all of you as it can prove helpful when making a business in RP!
I'm not 100% sure how accurate it is (so if someone knows a better resource please share!) but this seems to indicate it can help you determine the price of something using current cost and performing a bit of basic math to account for the inflation rates.
in case the site should disappear I'll quote the text from it below.
How Much Stuff Cost Long Ago A simple chart for determining how much inflation has effected the price of things based on the consumer price index (CPI.)
To estimate how much a loaf of bread that cost $2.00 in 2005 would cost back in the 1950s, multiply the 2005 cost by the ratio of the 1950s CPI divided by the 2005 CPI.
$2.00 x (1950s CPI/2005 CPI) = $2.00 x (28/196) = $0.29 or 29 cents.
You can also convert a price from long ago to today's equivelent price. For example, in the 1930s a record player could easily cost $200. To convert it to an equivelent cost in 2005, multiply the original cost by the ratio of today's CPI divided by the 1930s CPI.
$200 x (2005 CPI/1930s CPI) = $200 x (196/14) = $2800 (No wonder so few people back then bought recordmplayers.)
2010s = 237
2000s = 196
1990s = 153
1980s = 107
1970s = 54
1960s = 32
1950s = 28
1940s = 14
1930s = 14 (Note the sudden drop caused by the Great Depression. Also, this was the decade in which the government began its policy of deficit spending. From here on there is constant, and sometimes runaway, inflation.)
1920s = 18 (Note the sudden rise caused by runaway growth and investment.)
1910s = 11
1900s = 9
1890s = 9
1880s = 9
1870s = 11
1860s = 16 (The Civil war drove prices up temporarily.)
1850s = 9
1840s = 9
1830s = 11
1820s = 11 (The industrial revolution kicks in and drives prices down. The effect must have been amazing. In 1814 the index hit a momentary high of 0.12. By 1824 it dropped to 0.06. Imagine what this would mean to us if prices dropped so that in ten years everything cost one-half what it does today? A $30,000 car would only cost $15,000.)
1810s = 16 (Jane Austin started writing her novels.)
1800s = 16
Notice that from 1820 to 1920, except for one temporary and brief price increase in the 1860s, there was 100 years without inflation. This represents an era of unmatched stability. Three generations worked their entire lives without receiving, or needing, a cost-of-living raise.
The number for each decade was set at the average for that decade. In most cases this would have been the value at the middle year, for example 1965 for the 1960s. The CPI changes considerably over most decades. If you require the values for a particular year it'll be necessary to look up the exact consumer price index for the year in question.
In 2005 Mr. Tim Pickle emailed me the following information that may explain some of inflation's strange fluctuations:
Many people do not know it, but the dollar was redeemable in gold or silver until 1900 and then in gold until the 1930's. The value was initially set at 66.46 cents per gram of gold but this was changed by Roosevelt during the depression to 112.53 cents per gram which was a devaluation of the dollar and the real reason behind the drop you mention on your page and attributed to the great depression of the 1930's. In 1933 he also made it illegal for people to actually own gold, yet the mint made $20 gold coins until 1937 - typical government. By the way, those $20 gold coins are worth millions now because "all" of them were melted down because private ownership of gold was illegal.
We were supposedly still on the gold standard until the 1970's, but it was totally abandoned in 1973. Ever since the devaluation and outlawing of the ownership of gold in the 1930's and the deficit spending since that time the value of the dollar has slipped continually.