OP, personally I don't believe the financial aspect would matter for rapists...even if it were possible to implement something like that.
Your post touches on the topic for motivation for rape, and punishment, and the probably of being caught.
With respect to punishment, and possibility of being caught ... the sad reality is the punishment in UK to VERY light, and the probability of being convicted VERY small. The system is very biased in favour of the offender. It is depressing to think about it ... However, there is no point in complaining on forums, people who are genuinely interested in this need to actively support the services/organizations that are looking to change that.
There are a few theories on motivation for rape, if you want to read on the topic search for
A Natural History Of Rape: Biological Bases Of Sexual Coercion
and
Men Who Rape: The Psychology of the Offender
for two different (somewhat opposing perspectives).
Personally, I am an strongly in favour of DNA database for criminals, mandatory chemical castration for those convicted, much harsher sentences, a system that encourages reporting, and education so that people fully understand/respect people's right and the consequences of no doing so.
End of rant!