You can start with street shoes, as long as they (1) have a sole that allows reasonable turning [rubberized soles grip too much, some synthetics are slick and risk a fall] (2) have a back, or at least a good strap so you can actually stay in them without scrunching your toes [remember, you'll be going backwards a lot of the time] and (3) they don't slip and cause blisters. I'd almost add that they should allow you to flex your foot, but that can wait.
You'll want ballroom shoes in a few weeks, or at most a few months, so you're just putting off the inevitable, but that's OK in that you'll have a chance to decide better what it is that you really want. Be prepared, though. And eventually you'll want not just practice shoes but also a second pair for Standard and a third for Latin, all subspecies of the ballroom shoe. It isn't an inexpensive hobby.