Two words: Free Market!!
It's the same reason similar products cost varying amounts in shops. Goods and services are on offer and the producer or supplier of said goods and services value their product at a price they believe they'll get. No one is forcing you to buy it. It's a great system really. I mean, you have the choice to buy a Dell laptop and spend top dollar or you can buy an Asus laptop which will perform perfectly well for your personal needs for a significant lower price if it suits you.
If a lady can get €130 or even €500 for 30 mins then good for her. Why shouldn't she? The fact is the current market value on this particular service is on average €100 for 30 mins but that's not to say every provider has to stick to that number. Some go lower and some go higher. It's up to the consumer to decide how much he or she are willing to pay. The provider, however, runs the risk of pricing themselves out of the market if they charge too high for a basic service which can be got for far less money so in order to get the high sums of money they wish for, they have to provide an exceptional service to attract the kind of consumers who are willing to pay that price. It's the reason a Mercedes costs far more than a Fiat. There will always be a certain type of person who will go for the extras in life therefore the extras will always be on offer. You see, it's basic economics.
Hope this answered the OP's question.