i get mine done, pay £12 and lasts about 6 weeks, sometimes longer. should be ok for sensitive eyes as they will do a patch test with the dye before you have it done. a mixture of blue and black gives the most noticeable colour. the tips of my lashes are blond, so it really does make a huge difference when mine are freshly done. have always had it done professionally, but have recently bought a kit to have a go at doing it at home.
I get mine done and I hace sensitive fidgit-y eyes. I always seem to get the dye in my eyes and while it stings like the beejeezus for a little bit it is better after a bit. I pay about 10-12 pounds I think.
I've had it done quite a few times in the past and I love it. Can't quite remember how much though sorry. Also I don't suffer with sensative eyes so I can't be any help there. It does sting when you get it done but once you've given your eye's a good wash it's fine.