One of my favorite blogs to read is Copy Cat Chic. Reichel Broussard has an uncanny ability to find the "cheap" version of higher end furnishings and posts them on her website. I love finding new sources for more affordable pieces for my clients here. Mixing high and low is not only key to successful design, but it's more budget friendly. Here is one of her most recent comparisons.
I always advise my clients to invest in pieces that get the most use - sofas, breakfast tables, bar stools - as less expensive sometimes means not as good a quality. So once those items are checked off your list, then that's where the fun part comes in shopping for all the remaining pieces.
For rugs, I like using Rug Studio. They often have sales and shipping is free on almost all their rugs. They also have a very good search function that allows you to really narrow down the choices to what will work in your space. I needed an outdoor rug for a client who already owned furniture with orange/rust cushions, so I was able to search by size, style and color to narrow it down from almost 40,000 options to only 287. If you are ever unsure about ordering a large rug, order the smallest size they offer and use that as a sample. Your only out-of-pocket expense is returning it back, which is way less than returning a room size rug that wasn't all you thought it would be.
Another favorite is Target. Not only do I love shopping here for those great finishing touches - decorative pillows, towels, picture frames and lamps - it's also a great place to pick up accent pieces of furniture. Interior Fun came up with this amazing mood board with only items available at Target. The Nate Berkus and Threshold lines are some of my favorites.
Another great designer secret is taking ready-made drapery panels and adding some custom details. The easiest trick is adding decorative tape to the leading edge of panels like Chinoiserie Chic did here. Linen draperies give you the biggest bang for your buck and are available everywhere these days.