$250 k a month will only get you a USD9 million plane with 20% down, the lease on a E170/190 is going to be a lot lot more than this!
As stated , a basic assumption from 2013 rates as given under:
Aircraft Profile: Embraer E190 - Airfinance Journal - January 2013
How many will crash and burn in these startups , time will tell.
masalama.