If the purpose of your fitness training routine is to gain weight rather than lose it, go light on the cardiovascular exercise and focus on weight training. Not only that, it's a good idea to eat high-carbohydrate meals before training to fuel the extra muscle building you're looking for.
Don't fool yourself into thinking that fitness training requires a great deal of money and your own personal trainer. It's nice if you can get one, but with a little imagination and some research you can come up with your own fitness training course that costs you nothing more than a little willpower.