A blazer that fits like your favorite hoodie

Check out Uniqlo's https://m.uniqlo.com/us/product/women-soft-jersey-jacket-138942.html Right now the color selection is a little boring but they regularly restock so if you try it and like it you will probably have more options later.

I have http://shop.nordstrom.com/s/caslon-knit-one-button-blazer-regular-petite/4072864?cm_mmc=Google_Product_Ads_pla_online-_-datafeed-_-women:jacket_sportcoat:blazer-_-75657_1&gclid=Cj0KEQjwuqauBRDhnfvnxMvKy6UBEiQAmTLQu_S_MfSeb_A6m87Wo0ECUn_NeQ4dFrL90xNY404MiMIaAqHG8P8HAQ&mr:referralID=eebb88b3-402d-11e5-9ef7-005056941669 from Nordstrom's brand that is fairly form fitting and comfortable to wear. It may be a smidge too casual for what you're looking for, but is so amazingly comfortable, and I wear it constantly for business casual work engagements. I dress it up with skirt and heels, dress it down for travel days with jeans and flats, but it's one of my favorite jackets.

I have a few knit blazers from http://www.thelimited.com/online-shops/petites/petite-jackets-blazers?navid=top. I've also been eyeing this http://www.modcloth.com/shop/blazers-vests/fine-and-sandy-blazer-in-stone from ModCloth - it doesn't come in petite but it does come in lots of different colors. As a fellow petite person, I think that look for 3/4 sleeves will be helpful.

I can't vouch forhttps://factory.jcrew.com/womens-clothing/blazers_outerwear/blazers/PRDOVR~E1478/E1478.jsp, but I've bought similar knit blazers from J. Crew before and they were extremely comfortable and flattering. Since this is Factory it's probably unlined or crappily lined, but I never found that to be a big problem with the knit items like this. Look for coupon codes and you can probably get it under $100.

http://www.asos.com/women/blazers/cat/pgecategory.aspx?cid=11896&via=top&CTARef=ww%7Cheader%7Cproduct%7Cv3.

Have you tried LOFT or Ann Taylor? I've had luck with their pants and blazers in terms of comfort, fit, and durability. (I wear regular sizes on top and petites in pants -- bodies are weird.) http://www.loft.com/petite-custom-stretch-blazer/381417?skuId=19226286&defaultColor=&colorExplode=false&catid=catl000040&priceSort=DESC is a little over your $100 budget, but both LOFT and Ann Taylor have 30-60% off deals on what seems like a monthly basis so you could probably get it for significantly less than list price if you watch for sales over the next few weeks. I have what I think is an older version of that jacket and it has held up nicely for 3+ years and is very comfortable.

I just bought a http://oldnavy.gap.com/browse/product.do?vid=1&pid=602507002 from Old Navy and it is AWESOME. I never have a problem with Old Navy stuff and it wears like iron, at least for me. Wearing it with a nice tank or t underneath is like wearing jammies to work, it's that comfortable. The cut is very flattering. Comes in reg and petite. You can buy online and return online or in a store.

Petite here working in the tech side of financial services and seconding Suffocating Kitty's suggestion for the Caslon knit blazer. I bought 3 in different colors. I wear them every week at least once. Might be a bit too big on you, I had to get XXS instead of XS. I will warn you that it's unlined and as SK said, a bit casual.

I have narrow shoulders/a small frame and H&M blazers fit me extremely well and unlike many places are true to size (I have to wear an XS in Loft, Old Navy, Gap but am a solid 6 in H&M blazers). They come in a range of styles -- I would order a bunch and then return the ones you don't like.