If the CND acrylic course includes manicure and pedicure as well, this will be why you are paying more for the course compared to everywhere else. However, when you break it down to do the courses separately it wouldn't be far off the same price.
I forgot that NSI do training too, as far as im aware they don't have one course where you learn everything, so again it would be a case of buying separate courses to suit what you would like to offer.
You should chose a few companies of interest and research the company, the training and the products they use. Look for reviews on the products and training etc.
Make a choice which will suit your learning, everybody will favour one training company over an other so do some research and hopefully that will help you make up your mind a little more easily.
Don't be put off by cost of training, it isn't always the case the the cheapest training is the worse and the more expensive training is the best. However, you will only get what you pay for. Going for a cheaper course may end up costing you more in the long run and paying for an intensive 2-5 day course may not be enough for you after spending all that money.
it depends on how much effort you put in, and how much practice you put in after your training. Well in my opinion anyway. Some people can pick things up really quickly and others can't so find a course suited to your learning.