Interval/circuit training is your best option. How you go about that however can vary a lot.BTW: I know its requires a high investment. However, when one has limited time or funds the investment has to be well placed. So I should ask, with limited time each week what is my best option of building this stamina? Thanks again.
A relatively simple one I used to do was to do pyramid push ups. (Start with one push up, then go to 2 etc all the way to 24, then do another 24 before stepping it down backwards until you're back at 1.) In between the push ups, I'd do a pattern. The downside to that particular routine is that it took me about an hour to perform to completion.
Now I do a kettlebell routine 2-3 days a week and run ~2 miles on my off days. For flavor, I'll occasionally run the exercise course at the lake near my house.
In all, you're probably best off figuring a routine that works for you, and fits your interests etc.
http://www.sport-fitness-advisor.com/circuit-training.html