Is sewing about sewing in today's culture. And culture is really what it comes down to. If you grew up in a household that loved to sew like mine then you have a different take on it that somebody coming in new to the whole experience.
For example if you sew pillows, any type of cusions, even quilts it can be frugal, more so than buying them. And if you keep an eye open and didn't find them cheaper and especially if you would have gotten them anyways just make sure that you get a good deal on the fabric.
Clothes rarely are frugal, you can buy cheaper ones at the store unless it is a very specific/expensive item, costumes are a good example. But if you have never sewn before in your life there is little hope that you will achieve the quality that you will probably want.
For other things like some household goods it can get tricky. What I suggest is to go through it and spend some time calculating how much the fabric costs to make the item before you start getting your supplies together and trying to make the piece.
I used to knit and in many cases it can be cheaper, but there is a divide when it comes to knitting does often apply to sewing as well, fabric can be very expensive.
Before you rush out and load your shopping cart you should know, with sewing you have a fairly significant initial investment. This includes the tools, material and other odds and ends. I suggest getting a good pair of scissors, there is nothing more annoying than a pair of dull scisors.
Still how much you spend can vary greatly.
For me personally it isn't about the price, for some people it really only comes down to ho much it costs, I love good quality. And I have been very fortunate that I have been able to outfit my workroom with some of the best tools from thrift stores and even garage and estate sales.
One example is my velva-board. No one knows what a velva-board is or that their true value is. I found a brand new (it had not been used but was older) board that had I purchased it would have cost around $75, yet I was able to get it for $1.50 at a thrift store. I also purchase supplies from wholesalers, since it is far cheaper.
Most people will buy supplies from retailers like Walmart rather than those that service pros more than hobbiests. It used to be that most tools you bought, if properly maintained, would be fought over by your children when you died. Not today, with care you can make them last but they just don't have the same quality.
That is why I love the old tools that I find. They cost me a lot less and they will still outlast the new models you will find in the stores. Just make sure that if you buy an old sewing machine that it has more than thirty stiches.
My husband and I have talked about it and we like to compare learning to sew to learning how to take care and repair your car. Sure you can pay someone else to do it, but there is a potential for savings and the sense of accomplishment by doing it yourself is more rewarding.
That is why he has taught me to fix minor issues with the car and I have shown him how to sew.