If prices go up, the income that your prepayment earns will be used to offset any increase in costs. At the time of death, Eirene must provide a statement showing how much money is held in trust (including income earned) and what the services you requested cost at the time they are delivered.
Your legal representative will not be asked to pay more for the services or supplies you requested except for any balance that may still be owing under the contract. Any services or supplies that are requested but not included in your prepaid contract will also need to be paid for.
If prices go down, if the total cost is lower than the amount you pre-paid (and the interest earned since you signed the contract), then there will be leftover money. Any leftover money including the interest earned will be paid to your estate or the person specified in your contract to receive the refund.