Hello,
THis would need today to edit core files, and have enough skill in php coding.
But, i'm currently working on many registration improvements for next 3.7 version, where i will add a system for paiement (some features such as Paypal in pro versions only) and some of the needed options will be added to be able to set prices.
My goal is too, to be able to set different prices, for example children / adults, and so, the possibility to split number of tickets.
So, no easy solution today, but the next 3.7.x will allow much more for all! (check roadmap to get the latest news :
www.icagenda.com/docs/roadmap)
Best regards,
Cyril