The cheapest way to learn good technique is also the slowest and most risky - trial and error. Why are all techniques not created equal? Two big reasons: First, poor technique will limit your ability and quality of your playing. Second, poor technique can lead to repetitive motion injury and limit or halt your ability to play at all.
Since you write that you are trying to improve, you will probably be trying to improve for as long as you are playing, and that means you will be pushing yourself a little. Limits on playing ability will frustrate you and pushing yourself to practice more with poor technique increases your chances of injury. You can attempt more and more difficult pieces on your own and constantly try alternative techniques as you experience trouble with the pieces or discomfort after playing, but it's a bit risky and a long tedious process. I speak from experience.
You could try searching YouTube for technique videos but the best thing is to save your pennies and try to get a good teacher to meet with you at least once a month. Tell them that you are motivated to put in the practice and you really want help with technique and they should be able to address your particular hands and any existing bad habits in a way that any other resource can't.
I've never regretted saving and spending the majority of my disposable income on music.