Treadmills will end up being an expensive clothes rack. If you don't live in a condo and have neighbors under you, get some light kettlebells and look up cardio circuits on youtube. And don't be like most and think "oh... but it will interfere with my training and stagnate my growth." It won't because you are not going to be using very heavy kettles. It will work great for improving flexibility as well.
This is a good post.
I would say, for the most bang for the buck, an 80lb sandbag with two 40lb bladders gives the most flexibility in terms of conditioning options.
So many things - throws, cleans, hinges, swings, rucking, plyo jumps, etc......
If I was starting from scratch I'd go the sandbag or Goruck rucker, then add from there. They are so much more versatile and effective than one stagnant machine.
On topic, Sole treadmills seem to be pretty solid picks and are a lot less than 5k.
For 5k, you could put together an insane home gym.
