Best thing I would suggest go running but I'm not sure how you would feel about that but if you can go running like in field or even road if you are comfortable let me know and I'll tell you a plan of it.
If not don't worry you don't need to spend any money on anything even on pull up bar etc suggested in abive comment. Just do body weight exercises like pushups, an workout (you can find so many online and you could just search 4/5 different workouts and do them 4/5 different days. The best cardio workout you could do in home is burpees, star jumps, running in place .. maybe do this atleast 5 time or 6 times a week .. take 1 day off but please do eat clean as 70 percent is all about your nutrition and training is only 30 percent.. eat chicken breast, rice,eggs etc etc ... Best cardio workout I would suggest would be running but that depends on if you are comfortable or not .. you could train like athlete just like I do but you could get away with no gym ..