Not wishing to appear negative, because I'm not (honest), but if you're returning from a long break then you could just as easily have another break so to start with I wouldn't break the bank - just in case. Buy cheap until you've proved you're going to stick at it. Aldi or Lidl are always worth a look.
At this time of year, apart from a helmet which you already mention, you need gloves, padded bib tights (saves buying shorts), a thermal undervest (I've got some old Helly Hansens from my running days but there are loads of different tops around), a winter jacket and assuming you're going to be clipless you'll need shoes and overshoes. I'm a great believer in showing folks that cycling doesn't have to break the bank so a trip to Aldi is, at this stage anyway, maybe a wise move. You may even want something to cover your head, under the helmet, if it's cold and you have as much hair as me! If you stick at it then it's worth investing in better quality kit and maybe even a bit of bling like a Garmin or a pair of Oakleys (neither of which I've got, by the way, but I live in hope).
The list could go on and on but clothing-wise this would get you out the door and riding. We then go on to saddlebag, inner tubes, pump/inflator, nylon zip ties, tyre leavers, chain splitter, allen key tool......blah blah...zzzzz.
Not sure how much all of this would cost these days and no doubt there'll be a number of different responses to your thread, all given with good intent, but I'd take a wild guess that the list will be endless by the time we've finished, unlike your funds ;o)