You really don't save any money starting small. You WILL go big, it's not a matter of if, just when. You'll have money dumped into the smaller tank which could have gone to a larger tank. Yes using a 20g now will feel like you saved money, but, you will have tied up your $$$ in that when it could have gone right to the large tank you want.
I went right for a 150g as my first fish tank ever. My strong recommendation is to research a lot before jumping in to anything at all. I spent about 6 months really reading, watching video's (nobody has a good start to finish video out there worth watching, most add so much filler talk and never get to a point, that aside), and talking to people before I made my purchase. Even then I felt like I had no clue as to what I was doing when I did start.
To sum up! 20g is ok but bigger for first is way better! There is NO cheap way to do this hobby.
I went right for a 150g as my first fish tank ever. My strong recommendation is to research a lot before jumping in to anything at all. I spent about 6 months really reading, watching video's (nobody has a good start to finish video out there worth watching, most add so much filler talk and never get to a point, that aside), and talking to people before I made my purchase. Even then I felt like I had no clue as to what I was doing when I did start.
To sum up! 20g is ok but bigger for first is way better! There is NO cheap way to do this hobby.