My teens had iphones on virgin mobile and paid about $32 per month. We found that they did not have reliable service in all areas with VM. My son had a hard time getting a signal in his dorm room, and it was hit or miss getting on the internet using wifi. We also found the coverage area to be lacking when driving to my parent's house.
When the IPhone 6's were released, our family of 4 got a family plan with Verizon. We purchased the IPhones outright (would have to do the same with virgin mobile), and have 14 gigs of data per month for $140 plus tax. About the same price as the Iphones on virgin mobile, with much more reliable service and a much larger coverage area.