I'm going to be saying much of the same, but...
Its more of a hobby. Over time it will be "cheaper" but then again, are you just going to be making things because its cheap/free that you would have not made before? For instance... I needed a large seat bag for my bike. I found I design I liked online and made one out of materials I already had. It was free... for now, but the materials came from other progects that never happened or extra materials from other pogects (has anybody mentioned that wonderfull plastic bin full of fabrics, zippers, velcro and webbing that you will aquire?). Also, cycling jerseys have pockets on the back of them... everything I am now sticking in my seat bag could have been stuffed in my jersey pockets. So was that realy cheaper??? Who cares. I have a kick [Edited for inappropriate languge, please review forum policies for more information] seat bag that no one else in the world has.
Is it cheaper... kinda. Worth it... absolutely. You don't start sewing you own gear because you need item X and want it cheaper, you start sewing your own gear because you enjoy the geeky coolness of it.
The real money saving is if you do not have any gear or need to upgrade all your gear and are very patient in making it all yourself.
Scott