I don't remember the last time I bought a brand-new set of bed sheets. I just keep an eye out for really nice ones every time I go into Goodwill, and can often score an entire set in excellent condition for <$15.
Not long ago, I decided to turn an Ikea duvet cover into curtains for my bedroom, only to realize I needed more fabric than it would provide. The print was once very popular, but hadn't been made in years. I knew one would turn up at Goodwill sooner or later if I was patient. Three weeks (and $5) later, there it was.
I also got the most awesome full-length mirror (so I can make sure I don't look like a bag lady before leaving the house) for $20. It has this crazy, ornate Chinese-style frame that had some visible damage and was painted an ugly fake-bronze color, but it was such an unusual piece (that also happened to fill a practical need) I just had to buy it. I repaired the damage, repainted it lacquer red, and everyone who comes over wants to know where on earth I found it. I've never seen anything quite like it anywhere.
Knowing how to sew can be a huge money saver, as long as you keep an eye out for bargains on fabric. I've found some great fabrics at Goodwill every so often, including several large (6-8yd) pieces of Italian wool suiting fabric for about $2-3/yard (instead of $20-30). I've still got most of it stashed away, but I made three pairs of pants from that haul that look like I spent a fortune on them.
And speaking of sewing, I've bought all of my vintage sewing machines at Goodwill. Many times, I've bought them on special for $1.29, and only once have I paid more than $10 for one (that was $20 for a much-coveted Singer Featherweight). I've learned how to do minor repairs, cleaning, and tune-ups on old Singer and Kenmore machines, and when I get too many of them I sell them on Craigslist at just enough of a profit to make it worthwhile.
And then there's all the slightly damaged wool and cashmere sweaters that I can get for ~$3. I take them apart, unravel them, and knit, felt, or crochet them into other clothing or household items. I can't get yarn any cheaper than that (unless someone gives it to me for free).