Your best bet is to stable them just outside of the city. Westchester is a good area, very easy to commute to, it's just a matter of finding a reasonably priced stable. You'd probably be looking at anywhere from $400 for your standard feed, muck, turnout to $2000+ for the some of the high-end show barns, meaning they'll offer daily grooming, training, lessons, and services above and beyond the average horse owners needs. If you're looking for long turnout, you'll be searching through barns in the lower price range. The barn I work for charges about $600 for a professional on premises 24/7, box stalls, mucking, feed, extended turnout, and supplemental care ie. medicating, mane pulling, etc.
The most important thing to keep in mind is researching the barns you're considering. There's a lot of stables out there that will harm your horses sooner then they'd help them. Visit barns in person, look at all the horses they have. Are their horses happy? Are they in good weight? Are the stalls clean? Is the property safe? Ask lots of questions and trust your instincts. You couldn't imagine the condition horses will end up in when a barn just doesn't keep up on care.
If you need help finding stables, feel free to contact me! I'd love to help your horses to end up in the right place.