The values assigned to a driver in this competition are not a matter of opinion. It's all based on past performances and a mathematical formula. I'll do my best to explain it here. However a few points to note that may help with your selections.
The Maths
Each Rally will have a Number of Points Available which varies based on the number of stages and their length.
The total value of all the Fantasy WRC drivers participating in the Rally gives us the Total Driver Value.
So if the combined Number of Points Scored by all drivers for a Rally is 4500, and the combined Total Driver Value is 45.00, a driver is expected to score 100 points for each 1.00 cost. (4500 / 45.00 = 100). Therefore in this example a driver costing 2.50 needs to score 250 points to break even.
If the driver does better than expected and scores 350 points, they have scored 40% more than expected. The percentage gain is divided by 10 and applied to the drivers value. 40% / 10 = 4% increase. The drivers value will increase from 2.50 to 2.60.
If the driver does worse than expected and scores 50 points, they have undershot their target by 80%. 80% divided by 10 = 8% reduction in value. 2.50 becomes 2.30.
If a driver is not entered for a Rally their value is frozen until they next compete.