Sure, starting out with bag seed is a perfect way to go for a beginner, it's free and you can live and learn from the cheap seeds instead of the super expensive ones!!

As for the money you are going to put into it, you get what you put in. It can be a very expensive "hobby" and generally if you go cheap on what you give the plants, the plants will give you cheap results.

You may want to consider buying a HID lamp for your plants, maybe a 400 watter?