We get them at the shop at her opthamologist's office. They have a one year warranty on each the frames and the lenses, and they will give you new ones if the lenses scratch (which with a kid they always do), the frames bend or have any issues etc. Also, DD has a ski slope nose, so we are always having issues with having to have her glasses adjusted to keep them from slipping down her face etc., especially after she has had them a while and they have stretched out a bit, and those are all free. You definitely want to keep an eye out for that because if they look over their glasses instead of through them, it can cause issues. DD wound up having to patch for 2 months when she was in first grade because her glasses had been sliding down at school as she bent over her desk, and we didn't know about it. Turned out her teacher had noticed her looking over her glasses a lot, but didn't realize it was a problem she should tell us about.
We know several people who have used the cheap places and it turned out the prescription in the lense was not accurate, so if you do use the cheaper place, I would suggest seeing of your opthamologist's office can check the prescription and verify it.
We always do the anti-glare now. We didn't the first time around, and DD would complain about seeing rainbows a lot. The anti-glare made a big difference for her- she said she could see so much better out of them. It also looks a lot better in photos. We have done the transitions, but DD didn't like them because she says they do not turn back to normal fast enough when you go inside and she can't see when she is first inside.