I have an HD+ and love mine. At $149, it meets your price point and I prefer the larger screen but the 7" is even less expensive.
It works perfectly with calibre and with the Kindle for Android app, if you have Kindle books you want to read on it. Since it has access to Google Play, the closed OS isn't much of an issue, but you can also buy an inexpensive dual-boot SD card which allows you to run stock Android Jelly Bean without rooting or altering the stock OS in any way. This is the one I use and it works perfectly:
http://www.amazon.com/AndroidForNook...afn+nook+hd%2B