Yea choosing a board can be very confusing. You definitely want a womens specific board... mens boards are wider and stiffer. You should be able to find something for your budget if you shop around. I find this site to have the best deals on the web
Burton Snowboards and Skis, Burton Bindings, Burton Boots, and snowboard reviews. Of the brands you listed they all make good quality products, well except for sims really. Check out boards like the Salomon Lark or Burton Lux. As for sizing, it mostly depends on your weight so i cant really help you there without knowing what it is.