^ I agree.
If you really want to make 1000 bucks you need more than a month, or you need to find really good stuff: 1st editions of books, shoes, t-shirts, original art, cameras, collectibles, et cetera.
For example : that blanket I found cost 8.50. I could resell it on ebay for 100-150$. I bought a Big E (Levis) type 3 last week for less than 10$, considering LVC is over 200 I could resell it for 75 and make someone elses day, as well as my own. I bought a polaroid Sx-70 camera in the box, with a case, and a ton of ephemera last year for 5$, sold it promptly for 200$ on etsy.
With an initial investment of 100$, 80$ for merch and 20$ for gas I think you could make 1000 in a months time.
This would mean you spending friday afternoon and then all day saturday and sunday for at least 3 of the four weeks at thrift stores, garage sales, estate sales,scouring craigslist then if you spent Mon-Thurs listing the items on ebay/etsy/supermarket/market here you could come up pretty damn close to a $1000. There are a lot of great blogs out there you can learn from, just make sure when you search to use really specific terms 'thrifting' turns up a lot of girls with really crappy 'hauls' of 80's cat sweaters and LA gear sneakers.
Also, you need to have taste. This isn't something you can learn. You can find 'cool' stuff for sure, but having taste is critical. You have to assume everyone else in the thrift store is looking for 'valuable' things too. So you have to find niche stuff, stuff that's easily overlooked. I've made a ton selling mis-matched or slightly chipped Fire-King mugs and dishes. Most people will scoop up a set of 4 mugs if they're in perfect shape... but a slight chip and they don't want to pay 1$ a cup from Goodwill. I take those same mugs put up for 16$ with 8$ shipping (a deal on shipping) and they're gone! Fire King is insanely ubiquitous, but like Coca-Cola is sought after despite it's ubiquity.
If you're serious spend some time at the thrift stores, going down every single aisle walking through a single store about 3 or 4 times. You'll have to haggle some, you'll have to dig. It will be work, a lot of work but it could be worth it in the end.
honestly though if you NEED the 1000$ get a part time job tending bar or something, you'll make the money a lot faster and a lot easier too with less time involved IMO.
Also, you're gonna have to beat all the guys in this thread to the punch if you wanna make 1000