Target
I usually count on Target for basic pieces and great prices, but was sadly disappointed by the selection of mission-appropriate clothes. But it's always worth checking out because they are constantly getting new stuff in. They always have great basic tees, cardigans, and such. If you're going cold weather, keep an eye out for those colorful tights. They're usually cheap. Target also has great shoes but I would worry about durability and longevity...
Modcloth
I LOOOOOOVE Modcloth. I have had an account with them since... my freshman year of high school. But I never got to buy anything till now! Modcloth has very vintage-y styles (which is why I love it) which also makes them inherently more modest. I got some A-line skirts that are the perfect length and super cute. Make sure to read the reviews when ordering so you get the right sizes. Modcloth CAN be a little pricey, but it's a trade off for the quality. Also make sure you know what kind of care your items will need. A lot of their items require dry cleaning. Here's what I got:
Update: I ended up returning the boots; they were ginormous on my chicken legs :/
ASOS
WOW. Cute stuff. Great prices. Buy quick though because things go FAST on this site. Check out their "midi dresses". Here's what I got:
Shabby Apple
Again, more vintage styles. I hit them up for a couple cute blouses. I LOVE the peter pan collar style. The white shirt is a super comfy cotton tee, easy care, and the other is a stiffer cotton, also easy care. I got a 4 in both shirts but the one on the left was a little tight across the shoulders so I'm sending it back for a 6 :)
Forever 21
I can always count on Forever to have styles I love at good prices, but I can't always count on the quality. Be picky when shopping there. I did walk away with a couple blouses (long sleeve button ups and short sleeve blouses) and a nice plain black blazer. You'll need at least one blazer/jacket for baptisms. Watch the modesty at Forever too, they love to do backless things or cutouts where you least expect. But I mean, they always have about a zillion items (at least in our Forever21, it has 3 stories!) and if you're willing to take the time, you will find something that fits your needs.
Banana Republic
My mom hit up the sale rack in Banana for me. She came home with some cute short sleeved blouses which I LOVE. They are cute and comfy and easy to care for. Along with the short sleeves she found 2 long sleeved button up blouses, which I love to pair with my A-line skirts! She also picked up another blazer (navy blue this time) and two pencil skirts (which needed to be altered, but were still cheaper than the retail price #nailedit #goodjobmom).
Nordstrom Rack
Mom also found me some goodies at Nordstrom Rack. A chevron print maxi skirt, a plain black midi skirt, and two pairs of shoes that are QUALITY and will probably last forever.
THRIFT!!!
Thrifting is a great way to go if you have good thrift stores near you. I did get a skirt from DI (Deseret Industries) in Provo (love that place) for about $4. In terms of price, thrifting is great but make sure what you're getting is quality, and don't forget, CUTE. But try not to judge at thrift stores, you don't always know a piece's potential until you pair it with your own wardrobe!
Basically... you don't have to dress like a granny on your mission. Buy clothes that you WANT TO WEAR. Just be smart about it!
*update*
I was having the hardest time finding/ choosing a bag that I thought would be appropriate for the mish. I didn't want to spend a lot on a nice leather bag and jack it up, or get it stolen or something. But I was afraid of buying a cheap bag that wouldn't last! So here I am 6 weeks out from heading to the MTC and a miracle happened! I FOUND this bag in a closet at my house. Apparently it was my mom's old purse (I think it was originally my dad's old briefcase). Anyway! It's super cool! It's made from leather but I won't feel bad if it gets trashed because it's already old and forgotten (not to mention free). SCORE! And you might not have a hidden treasure like this lying around your house but it's worth a look!