Everybody does their finances differently, but if you need to contain costs, your best bet is to allot yourself a strict and generous budget. The first few years of any hobby involves a fair amount of purchasing.
The other approach, one that I will be using for the next couple of years because I have too much stash, is only buying to finish projects already started. I have an expensive sewing machine that sucks up all my hobby budget until it is paid for. That will be followed by another, but less expensive 'class' sewing machine (lighter weight). I can only afford these IF I limit my purchases.