You should check the clearance racks first even though they're probably full of the clothes from last season that nobody wanted. However you may find some perfectly good clothes at great prices.
Shop ahead. If you know you have a special occasion coming up, and you need the perfect outfit, start looking well in advance. This gives you the opportunity to check all the stores and even order online. Wait too long, and you could have to settle for whatever fits. In most stores, the plus size section is a lot smaller than the 'regular' clothes, meaning the selection also leaves something to be desired. Look for clothes that can be used elsewhere. This won't reduce the price of any individual garment, but it does mean that you can make part of your budget do double duty. If you can find a formal dress that doubles for work, part of your problem is solved.
Don't just stick with one store. Sure, it may be your favorite, but if you don't know what else is out there, how can you know you got the best deal? If it fits your budget, get the top at one store and the shoes at another. Avoid trendy brand names unless they denote quality. Some brand name clothes are actually assembled better than their generic cousins. However, a lot of the time, all you're buying is the name. Money conscious plus size shoppers should keep an eye on price markups that come with a famous name.
It is tempting to buy an item based only on price. But be careful not to go too cheap, because you want that special occasion garment to last for more than one wearing. You'll need to be especially careful of this with plus sized garments, since it takes more time and energy to find ones that fit well and look good. Be aware that quality it important. Spend your money on quality garments and you won't have to buy another one for a long time.
Watch for sales. If your favorite stores send you sale flyers, you can plan to shop when they offer the best bargains. There are plenty of other tips for shopping for a fabulous plus size outfit, but these will get you started. It is important to pay attention first to quality and fit, then cost. And remember - the bargain rack can be your friend!