Assume, if i want bid at least
100 g for his value
+ 800 g for wage
+ 30 x 800 g for Signing on fee
That mean I must pay 24,500 g !!!!
This is over unrealistic price.
That's why the signing on fee is better if we take salary difference x 30. That means next regarding to your example:
Asking price: 100 g
Asking wage: 800 g
You offer:
Transfer fee: 100 g
Wage: 900 g
Price will be: 100+(900-800)x30=3100 g, which is not too high.
But if you offer hudge wage like 10000 g, then final price will be:
100+(10000-800)x30=276100 g
That rule will definitely prevent absurdly high wages.
But if the rule stays wage x 30, it will be impossible to by players with naturally high wages, which means it will be impossible to by players with high CA!