I just bought a pair of hair scissors from Target's hair dept.  They were diamond sharpened...the higher end of two choices.  I think I paid $20 or so for them.

Your best bet is to go into a Sally's or other beauty supply store that sells to everyone and talk to the girls there although I will tell you more often than not the more expensive the shears are the longer they will stay sharp (or be sharp for that matter) and the better they will cut. Try not to buy shears in the $10-20 range as they are usually no more than glorified kitchen scissors. I have a pair I bought from sally's for work (I am a hair stylist) for $89 about 2 years ago and they are still sharp and cut a good clean line and I use them pratically everyday , and usually if you spend more money on shears you won't need to sharpen them as often (and please dont EVER try to do that with the kitchen knife sharpner) or replace them as often saving you money in the long run