Offer from MM IBD London- No mention of Comp.

So I got an offer for SA at a MM in London but it did not include any details of pay (got it through the MD who I met at an event). I asked his assistant for more details but she said that HR would take a little more time in order to have my contract ready since they also need to sort out my Visa formalities.

Question: What is the best way for me to ask the PA regarding the salary, I know she probably can't give me an exact figure, but I need a ballpark figure to see if I can afford it... London can get very expensive.