( Target cost 100k, FA 150k)
If the target (total of the Prices) is exceeded, then the Contractor shares the overspend in line with the percentages outlined in Contract Data part 1. If for example the Contractor share for anything over the target was 50%, then the Contractor would be paid £125k using the numbers in your example. If the Contractors share was 100% for anything over the target then they would only be paid £100k (but then again knowing those percentages at tender stage would have meant the target would have been set higher in the first place) .
This is the pain/gain principle of option C. Contractor “shares” benefit of any savings below target but limits risk to some degree if they go over - the amount of benefit/risk being purely dependent upon the percentages identified in contract data part 1. The Employer needs to consider carefully prior to tender as to what those percentages should be to encourage the behaviors/risk profile that they are looking to achieve.