To celebrate my first 50 lbs. lost, I'd like to add to my home gym/outdoor workout collection. I have a bike that I love, dumbbells, a step (for stair-stepping inside), resistance bands, an exercise ball, and good running shoes. I live in an apartment (second floor) and have 3 small kids so anything huge or requiring good storage is out. It also needs to be relatively cheap.
So, with these limitations and with the desire to add some variety to your work outs, what piece of exercise equipment would you purchase to celebrate?
Thanks in advance.