what is a good adult beginner dirt bike?

[Brian]

i am 26 years old and 6'0 185 i just started riding over the summer iI bought a mini baja dirt bike. quickly out grew that and my wife liked to ride so i gave her that and went and bought a used 1990 yamaha rt 100. i loved it it wasn't too powerful but it still went fast. then 2 weeks later things started going. I've paid $400 for the bike then 50 in clutch and clutch cable parts then 100 at the dealership to set the spring on the side cover. the whole side cover has to come off to do the clutch. so after all that i get it home and the clutch doesn't feel right but a buddy told me it that was hoe a new clutch felt. so then after a hour riding with my wife not hard at all i didn't shift past 3rd the starter feels like it won't grab and i can't start the bike. so i'm looking at a new bike maybe brand new. I'm looking at the 08 yz 125 ($4600) vs 08 crf 250r ($4600). i have plenty of land with hard dirt, soft dirt, hills, trails, it's a 600+ acre wildlife preserve. No Jumps but many bumps 1ft high I was also looking at the 09 yz 250f for $4700 seems like a good price for twice the bike i dunno also not sure if i will get boredmaintenance125 fast or not. I have been told that. But i want a good low maininance beginner bike i can have fun with for at least 5 years before moving up. thank you