Just buy a MacBook Air and get a desktop for $1000, will be more than enough to max out any game at 1080p.
This is only a good solution if you are willing to take the compromise on the MacBookAir not being that powerful for other Mac tasks compared to a rMBP.
It's not always the best solution if you want a Mac that will last a long time and so you can play games. Just offering another viewpoint, I can see both sides on this one