I do not like working on my stuff. I work on others stuff enough so I always go for new or newer and never keep past 150,000 miles. Thats just me.
Sounds like you want to keep it as cheap as possible. My neighbor is a commercial mower, 1 rig with 3 mowers. He runs a 2007 truck. The thing is if you are mowing you can not afford break downs if you are a 1 man crew. With rain in the summer and spring 1 or 2 days in the shop can put you a week behind. He has ran into this even with his 4 year old truck twice now. Luckily we are good friends and I have 3 vehicles so I have loaned him one to keep going on them occasions.
I have another friend that runs a large landscaping/mowing business. He buys 8 new F-250's with plows every 5 years. They simply just wear them out. He has some older stuff like Broncos for plowing and Class 5 though 8 trucks for other uses but the ones he uses every day, rain snow or shine he needs to be reliable.
Chris