Timothy - me sermons bears little resemblance to me mobile phone (except when I forget to turn it off and it goes off during one). You'll have to come some time and sit through the agony...
O2 publish the rates, so you can know exactly what you'll pay to use GPRS with any particular network in any country. That's the first link above. I'm with O2 so I'm happy at that point.
Voda, on the other hand, keep it secret - that's the best their website can do.
My only suggestion is either:
a) assume Voda is similar to O2 in what it charges, or
b) change networks to one that does know, and can tell you, how much things are going to cost.