In this sentence, ska means "should" (meaning "have to" or "shall" -- you absolutely have to pay). Borde is used for giving suggestions or recommendations.
"How much will I pay?" pretty much means the same thing as "How much will I have to pay?".
Seeing as the writer is usually very punctilious as to exact translation, i would expect the future here, as pointed out by trevro above
This isn't the future tense, it is the modal verb ska. If it were simply future, we would have said Hur mycket kommer jag att betala?. ('how much am I going to pay')
So ska here has the meaning of should, ought to or even close to must. But it's hard to translate into English since the languages don't work exactly the same here.