To be honest, if you are concerned about saving money by tying your own flies, don't bother. The main reason 90% of us tie our own flies is because we want the pleasure of catching fish on something we created ourselves. There is nothing like the feeling of that first fish you catch on a fly you tied yourself, and the feeling continues with subsequent fish. But to tie in order to save money... well... unless you use EVERY bit of feather, fur, and mylar you buy, and then use ever single fly, you're not going to save money. Commercial tiers only make money due to the fact they can tie fast and use all their materials. Otherwise, it's money down the drain.
So, in the end, don't begin tying to save money. Begin tying to be creative and control your fly box.