I also get stressed out by looking for a good deal or searching around in used stores for the things I want. I don't have time to go to them over and over in hopes of finding something I wanted. I also don't want to fall into the thrift store trap of "Oh, but it is so inexpensive!" and buying things we don't need. But I'm getting better at trying there first.
When we recently decided we needed to get Big Sister some new puzzles because she is in a puzzle phase, I was pleased that my first thought was Goodwill! So we went. And then we realized we needed some shoes for her as she's all of a sudden grown and her shoes hurt. So for just under $14 we got a pair of boots, a pair of sneakers and 4 puzzles!
We've done 2 of the puzzles and they have all their pieces, plus two extra from a puzzle we didn't buy. Extra is better then not enough!