How do I buy Illinois RV and get it to New York?

You can get a temporary transport slip, even in NY. I bought a Mazda MX5 online, flew to Long Island one morning, inspected the vehicle, paid and got the title signed over ( was even actually a Maryland title ), went to NY DMV, had my insurance company fax info to DMV, got a temp tag to transport from NY to NC and was on the road home before 3:00 pm. Just contact your ins company and local DMV in advance. I think you can do it and drive it home.