I am planning to do HIIT and want to buy one (cheap, under $100) piece of equipment for the whole body.
I cannot sprint because I live in a busy city with few open spaces, however I would be fine with equipment like a suspension trainer or skipping rope.
I'm not a beginner, and wouldn't mind high impact exercises.
Please do not recommend bodyweight exercises — they are just not for me (I've tried), and not what this question is about.
If your piece of equipment has any other benefits (eg. portable, scalable), please put that in your answer as well!