@TenaciousGoat - One of the best fitness investments I've made, is a set of adjustable dumbbells. With a handle twist you can adjust them from 5-50lbs.
They were a spendy $300, several years ago. But I justified the purchase because they were compact, and fit in well with driving a semi cross-country.
But the investment could be easily justified by the convenience & speed of adjustment alone. That makes it less of a hindrance to use them, and all the fiddling with weight adjustments adds up.