Outside of negotiating my actual salary, the next hardest part was figuring out what currency my compensation would come in.  Since he said that he would be paying me in raels, the appropriate calculations had to be made.  Raels were a Spanish currency, and Spain had a different currency system from the rest of Europe.  See image on side for photo of reales.

34 maravedis = 1 reale
8 reales = 1 peso

Then the site goes on further explain that 1 reales was worth 6 English pence or 5 Dutch stuivers while the country suffered sufficient inflation during the time.

There were two ways that we could have figured out how to convert shillings to reals:
1. Calculate the mass of the metal used and convert it to market value
2. Research the period conversion rates

Spanish reals or real de vellon were produced in 1600 by King Philip II, and were made out of silver weighing approximately 418.0g.  The first method would be a helpful guideline to use, but it didn't account for inflation.  

To further calculate the conversion, I used this online calculator created by the Pierre Marteau Publishing House, which converted my salary according to the Paritus rates of 1709:

1900 Spanish Reales = 51 Pounds
Calculations using Marteau calculator: 109 Pounds, 50 Shillings = 4153 Raeles, 31 Maravedis