I will try and answer your question but this involves different types of currency that I am unable to give you an adequate exchange rate to modern currency but can tell you how manageable or unmanageable it was to pay for the ransomed people.

In this time period of warfare, ransoms for nobles played an important source of income for the ransomer during conflicts. The norm was to capture nobles alive for this reason. Of course killing of nobles did happen but they were mostly due to the normal course of a battle and not specifically intended incidents. Of course purposeful killings did occur like at Battle of Evesham(1265) in the Second Barons' War where Simon de Montfort along with his son Peter and other leaders were purposely killed. As well during the War of Roses, killing the noble leaders became a normal course of action which is why that conflict evolved into ongoing blood feuds between Noble Houses that opposed each other in the claims of the house of Lancaster and York.

During other conflicts of the period such as the various conflicts encapsulated in the Hundred Years' War, ransoming or just leaving imprisoned problematic nobles or Kings was the normal course of action, such as the long confinement of King David II of Scotland in England for 11 years, his ransom was 100,000 marks which 10,000 supposedly would be paid yearly starting in 1357. David was released to raise the ransom but due to the burden that it had on Scotland could not be completely paid and he decided to come to a different accord for peace to have the debt cancelled with the English.

King John II the Good of France on the other hand was held captive from 1356 until the treaty of Brétigny(1360) where he was released in exchange of hostages that included two of his sons so he could return to France and raise the ransom of 3 million crowns or Écu. Of course this ransom proved to be an onerous amount to France. The last payments of which would be payed until the reign of King Henry V of England, leaving 600,000 crowns left unpaid(Anderson 190). King Richard I the Lionheart of England ransom was 150,000 marks in the year 1194 which was at the time 2 or so times more of the annual income for the English Crown at the time.

The exception to the norm was when ransoms were payed for non-nobility. The fate of commoners depended on the circumstances of the war. It could be recruit into the opposing forces, executions by the victor, or sold into slavery.

One of the few incidents that a ransom was paid for the non-nobility of a conflict is in the Siege of Jerusalem(1187). In the aftermath of the battle of Hattin(1187) where the bulk of the army able men of the Kingdom of Jerusalem were defeated, Saladin led his army in conquest of the Crusader States. In Jerusalem, Balian of Ibelin was in charge of defending the city. Balian and Saladin handle their negotiations through a native Orthodox scholar named Yusuf Batit. Of note before Balian had arrived the citizens of Jerusalem had sent a delegation of their own to negotiate with Saladin. There was some wrangling where Saladin first asked that he would let all go who could pay ransom which was 10 dinars for men, 5 for women, 1 for children. Balian said that there were 20,000 inhabitants who would not be to afford such a ransom. Saladin then offered 100,000 dinars should be the amount for a mass ransom of all those who could not afford the ransom. Balian said such an amount could not be gathered and they came to an agreement of a mass payment of 30,000 dinars for the freedom of 7,000 of the inhabitants. The Latin Patriarch Heraclius and clergy payed their own ransom and as did the Holy Orders of the Templar and Hosptillar and then carted out of the city the valuable items of their institutions from Jerusalem. Saladin's brother al-Adil was bothered by this sight and asked Saladin for 1,000 slaves as his reward of the spoils, he then proceeded to free all of them. Heraclius then asked for 700 slaves that he then liberated. Balian received 500 slaves of which he liberated. Saladin then announced he would release all the aged women and men. Women who managed to ransom themselves then came to Saladin to plead for freedom of their captured husbands and fathers to which Saladin granted. Saladin as well gave from his own share of spoils an amount to every ransomed widower and orphan. Keep in mind that these were only the Latin Franks that were being ransomed or enslaved. The native Christians, Jews, and such were allowed to remain in Jerusalem because Saladin wanted a bloodless and intact capture of the city. The rest that remained were led into slavery(Runcimen 463-467).

In summery of all this the negotiated were usually handled by a delegation from each side and sometimes even by the leaders. Those who were ransom were generally the nobility and the fate of the commoner was usually recruitment, execution, or slavery, the last two of which were more common in wars that weren't internal in nature. The amount of ransom would increase depending on the rank of the nobility and with how prosperous those nobles were. Inflation did occur but that is outside of my range of knowledge so the amount that was paid in 1100~ ad would be different to an equal amount in amount of that particular currency some hundred or so years later in the same region.

Anderson, A. (1764). An historical and chronological deduction of the origin of commerce, from the earliest accounts ... Containing, an history of the great commercial interests of the British empire. To which is prefixed, an introduction, exhibiting a view of the ancient and modern state of Europe; of the importance of our colonies; and of the commerce, shipping, manufactures, fisheries, &c. of Great Britain and Ireland: And their influence on the landed interest. With an appendix, containing the modern politico-commercial geography of the several countries of Europe. London: Printed for A. Millar.

Runciman, S. (1987). A history of the Crusades, Volume II: The Kingdom of Jerusalem and the Frankish East 1100-1187. Cambridge: Cambridge University Press.