I know there's all kinds of training aids availible on putting, chipping, swinging, etc but I'm wondering if there's really any known training aid that's proven to be effective. Hopefully something that doesn't cost over $150
Since alignment and stance really are fundamental in putting a good swing on the ball, practicing these over and over until they are second nature can certianly be done indoors. I also will practice on target lines I draw onto a piece of cardboard to make sure that the shoulders are parallel to the target lines, and so on. If you want to practice swings in a low ceilinged room, I find that choking up on the club (way up to maybe only 6 inches or so above the head) is very similar. Plus, it trains the hands to stay in front of the impact, else the club smacks you in the side if you flip your wrists under the ball.
I have an eyeline putting trainer (mirror with lines that lays on the floor) and that has helped with my putting setup and alignment...putting feel for me is still only really developed on the practice green however...