My 150 watt HPS M250R2 cost me around $150 I believe, from Graybar. That was a couple years ago though. I too have noticed the prices on Grainger's website are ridiculous. However, contractors who have an account with Grainger probably get a better price, as they usually buy in larger quantities for jobs.
I will warn you about the AEL fixtures. It seems their quality is going downhill. Nearly all of the newest 115's here have broken refractor door latches. When I'm driving around, I see 115's all over the place with missing latches, and their doors taped closed. I just saw several tonight, along with one with its door open. The open one still had its latch though.
I still like AEL cobraheads though. They just need to watch their quality control.