The vortex strikefire is a high end budget optic. That's about $150 used.
I put one of these on my AR. Good optic. Comes with a 2x magnifer you can screw into the rear eye piece and you can switch between read and green. I think i got mine new for between 150-200 new from opticsplanet.com but that was at least a year ago. The only problem I have is that the dot will obscure targets beyone 100 yards. At 25 yards on a normal man sized target the dot will completely obscure the head but if zeroed properly will still tack right in the middle.