I am 14 years old I am about 5'5 and l weigh 100 pounds. I am looking for a good brand of skis that are still cost effective, I am at an intermediate level.How much will they averagely cost? (skis,bindings,boots,helmet,poles? And how long should they last for?

Let is start with a high budget & break it down from there.
Go to a ski shop, try on several different brands of boots, write down the brand, model & size. The boots r the most important part of ur equipment. u need an intermediate boot that should last u 2-3 seasons before u outgrow them for size & ability. They then need a set of custom foot beds so ur feet r comfortable. Total should be $3-400 for the boots & $50 for the foot beds. Also get checked for cants & delta. This now will let u be comfortable all day in the boots.
A pair of good skis with bindings, should be about 150 cm & the bindings need to fit ur weight & ability. You r at the upper limit for a junior ski, but the bindings need a DIN range of 3 to 10. A good new pair of skis & bindings can run $400-$600 & up. A helmet can be $50-$100, poles about $50.
So the total budget for new could be $1000 to $1500. Most of the skis & bindings can be purchased in ur size on Ebay for a big savings, u will progress & replace the skis in about 2-4 years, the boots about the same time.
Some of the Ebay sources have K2-4R with bindings for $90 or there about. The boots u will need to shop for, Ebay, C list & the local ski swaps. Good luck have fun.

l am in the same boat, just heavier. l would recommend Volkl skis. l have skied on them for a while, & they r amazing skis. Boots, see a good bootfitter (They run in different sizes pending on manufacturer; l use Nordicas because they run wide, for example) . Rather than buy skis & boots, some ski shops will lease them to u from season to season, so u do not outgrow then u should buy some good skis/gear. Buy & keep ur helmet, as that is one of the more important things. l personally like my giro helmet with the headphones built in. As for poles, u should also buy ur poles, but l would reccomend Scott poles.

k2 atomic volkl dynastar for decent for the whole 9 yards 350 -500 give or take

From my experience the best skis l have ever skiied on r Rossignol or Atomic.
l am not sure whether u would want to get skis at ur age, as u would outgrow them, & the more u ski the better u will get so intermediate skis wo not suit you, u will want something better.
My advice for someone ur age is to rent skis, they may cost a bit extra but u can rent the same seasons models, & they r not going to let u down. l am 20, & have just bought my first set of skis.