Kettlebells are a very good option. I will say, however, that they’re typically more expensive than a dumbbell, and there’s very little you can do with a KB that you can’t also do with dumbbells, and you will pretty quickly get stronger, initially.

Rowing machine is my votes I’m a Concept2 fan; they make great equipment. They’re in the USA but the company is a Perpetual Purpose Trust, so it’s different. I’ve heard good things about WaterRowers too. You’ll be able to test a concept2 at nearly any decent gym, as they’re the standard rowing machine (and thus will last virtually forever). I recommend testing, extensively, if you can.

Treadmills, to my knowledge, are expensive if they are going to last. They’re heavy and large.