UK, 1814

At cited 1814 prices, it appears the London platina price was ~50% higher than the US rate, at varying USD currency exchange rates (£ 0.2081 - £ 0.2438) on the Eastern Seaboard.

Assuming a High in early 1790, @Fr 27.125 per £ 1. and a Low @Fr 25.02:
 
1790?: 1 Troy Ounce Platinum (mkt, refined ingot) = £ 2.50 (Fr 67.8)
1804?: 1 Troy Oz. Platinum (mkt, refined ingot) = £ 1.50 (Fr 37.5)

1808?: 1 Troy Oz. platina (whols., Colombian ore) = £ 0.20 (Fr 4.88)

1814: 1 Troy Oz. platina (whols., Ore 70%) = £ 0.15 (Fr 3.15)
1814: 1 Troy Oz. Pt (intrinsic, Ore 70%) = £ 0.2143 (Fr 4.50)
1814: 1 Troy Oz. Platinum (Producer Cost) = £ 0.3143 (Fr 6.60) 

1814:  1 Troy Ounce platina (Est. Choco Spot) ~ S$0.1014 (£ 0.0225)  
1814: 1 Troy Oz. platina (Est. Cartagena Spot) ~ S$0.1352 (£ 0.03)

1814: 1 Troy Oz. platina (Jamaica: bulk, whols., ore) = £ 0.07034 - 0.08239

1814: 1 Troy Oz. platina (US port: bulk, whols., ore) = £ 0.08561 - 0.10028  
1814: 1 Troy Oz. Platinum (USA: Bollmann) = USD$ 3. (~Fr. 15.24)

February, 1814: 1 Troy Oz. Platinum (mkt, ingot) = £ 0.75 (Fr 15.75)

This serial of Rees' The Cyclopædia dates to February 1814. A"few years ago" elsewhere in this section refers to +10 years, circa 1800. Subsequently plagiarized by Encyclopaedia Londinensis, or, Universal dictionary of arts ..., Vol. 15 (1817) p.478-9 and other works.

This metal may now (1814) be purchased in bars at the rate of 15s. an ounce; whilst a few years ago, its price was between two and three times as great.  The price of platina, in grains, fluctuates between 3s. and 4s. an ounce.

Citation: The Cyclopædia: Or, Universal Dictionary of Arts, Sciences..., Vol. 27 Abraham Rees (1819)

 
 
1814: 1 Troy Oz. Palladium (Trade: Cary) = £ 4.20 (USD$ .)

1814: 1 Troy Oz. Palladium (.999)  = £ 4.70 (USD$ )
1814: 1 Troy Oz. Palladium (Est. Retail: Cary) = £ 4.90 (USD$ .)  

1814: 1 Troy Oz. Palladium (Est. Ret.: .999) = £ 5.50 (USD$ .)

When the Market Price for standard Gold was £ 4.- 4.20, Dr. Wollaston paid £ 4.40, a premium of 5-10%.  If Wollaston charged £ 0.75/Ozt., he sold at less than one-sixth the equivalent price in Gold.

8/1814: 1 Troy Oz. Gold (Mkt, .999) = £ 4.3636 - 4.5818 (Fr 101.26 - 107.21) 
August, 1814: 1 Troy Oz. Gold (Trade, .999) = £ 4.80 (Fr 106.08 - 112.32)  
  
"From an invoice preserved in Wollaston's papers (14) we know that in August 1814 the price for gold purchased from a London gold and silver merchant was £ 4. 8s. an ounce; so Wollaston sold his platinum at less than one-fifth the price of an equivalent volume of gold."


In "Justus Erich Bollmann and Francisco Antonio Zea" Platinum Metals Rev., 1983: 27,2),
Chaldecott mis-dates Bollman's information: "Adams, Robertson & Co." was the firm's name in 1815.  At that time, Wollaston well-stocked, paying less and easily acquiring platina - the market was saturated, not in scarcity. 

In all probability, Bollman's comment dates after 1817, the period when he was in London but struggling financially, in debt to Wollaston and revealing his platina sources.  

  Bollmann first made Wollaston’s acquaintance when he called on him in London towards the end of August 1814, shortly after arriving in England on a journey from Philadelphia to Vienna (5). This was the time when he told Wollaston that supplies of crude platinum could be obtained from the merchant firm Adams, Robertson & Co, of Kingston, Jamaica, and that smuggled ore could not be bought at Cartagena for less than five Spanish dollars a pound avoirdupois, equivalent to 1s. 6d. an ounce troy, and that the price at Philadelphia was six dollars (6).