I know your probably asking girls on this but hers my opinion. Whats the point of them? My self and the large list of guys i have talked to on this subject agree that they do nothing in terms of us being attracted to a girl. Thats not to say that in an overall way they did not play a part. I know i have yet to go up to a girl and be like, " wow girl your eyelashes are beautiful. Guys prefer natural beauties who wake up the same way every morning with out having "to put there face on". Now if your doing this for personal reason then go for it.
I have seen pictures of girls who have had them done, and for the ones I have seen, I think they look great! Not the ones that actually look fake, but the ones that look really natural, but yet long and filled at the same time! I have had them done at MAC before, for prom, and they looked good, I just wished they looked a little more natural. I say, do it :)
Eyelash extension prices start from $100. It really depends how long you want them (as the longer you get them and the more they put on your lashes will give you the overall total on the price) Make an appointment and allow an hour and a half for them to be put on you. Don't splash water on your face. As that may make the lashes come off. They will tell you to use a towel and slowly wipe around your eye area.
Eyelashes tend to fall (which is natural) so whenever that happens you will need to go back and get touch ups, which will cost more money.
Overall they are nice, but they can damage the existing lashes you have.