You can definitely apply. The danger you face is that Maths Studies is often regarded as a course where people have elected to decrease their course load (because unlike the SL/HL comparison, Studies counts as SL but is easier).
In general, for premier universities you want to demonstrate to the institutions that you’ve taken the most rigorous course possible, regardless of if maths is part of your desired degree. For Economics, you’ll need calculus at University (economics becomes calculus at a high level), so I’d recommend at least SL Maths. Many places ask for HL.
I’d advise at least trying SL maths. If it’s too hard, then you might need to take the risk, but I’m sure with hard work you’ll be fine in SL!