Not another "what bike should I get" thread (it is)

Hi all. Just came over after years on vitalbmx. I'm getting older and am feeling like its time to officially transfer over and take mtb riding serious. At the moment I'm on Mackinac island which is bikes only and horses. No cars. So I've become well acquainted with my 1999 Mongoose Maneuver. Its an awesome steed (to me) even w it h only back brakes on it. I ride this thing to work, for fun, and I even hit some nasty trails on it. I do anything with the thing. But I know I'm limiting my experience and capping my potential with it.

So I'm looking to sadly upgrade to something that will maybe cut my work load a tad bit to say the least. Something mid range/entry level. I ride roads A LOT so I would like for it to be road friendly. But I also wanna be able to charge through some trails too! I don't intend on spending a ton, or even a lot. Realistically any modern ride would be an improvement. I'll put my price point at 550-720, but preferably low as possible. It hasn't gotta be the best as I am plenty capable of replacing things along the way!

I just want something with a good frame and upgrade path that'll let me experience things a little more properly. I don't mind it its older either if it'll increase value.

Thank you in advance
-EDIT_ I am 6 foot 1 also.