The Nexus program has always been very interesting because it shows the Android operating system in the way Google intended in hardware that meets the expectations of the software maker, besides, these devices are the first ones to get the latest version of the OS. It started with premium devices from HTC and Samsung, being the Galaxy Nexus the first phone that introduced on-screen buttons included in Android 4.0 Ice Cream Sandwich. Then, after the unsuccessful release of Android 3.0 Honeycomb, Google decided that the software was mature enough to run on phones and tablets alike and introduced Android 4.1 Jelly Bean along with a 7 inch tablet called Nexus 7 made by Asus. The twist, it was priced at $199 and it offered decent specs for the time and even a display with higher resolution than some other tablets.
That fact set a new trend for the Nexus program, when Google chose LG as the maker for their next Nexus phone, the Nexus 4 came along combining decent specifications (good, but slightly outdated) with good design and, most importantly, a price that started at $299. It was 2013 and Google introduced a second-generation Nexus 7, it featured a much upgraded hardware like a display with the much higher resolution of 1200 X 1920, a camera in the back, stereo speakers meant to work in landscape mode and even wireless charging in a thinner and lighter body. The base model doubled the internal memory and was priced slightly higher at $229.
The last device to integrate good specs and a low price was the Nexus 5 with Android 4.4 KitKat which started at $349. The future of the program was uncertain until Google announced the Nexus 6, a 6-inch phablet made by Motorola that has some of the best current specs but costs $649. At the same time, a tablet called Nexus 9 was announced, made by HTC and integrates the recently announced Tegra K1 processor and a 9 inch and its price starts at $399. Both of these devices came with Android 5.0 Lollipop out of the box.
Now, it has been reported that the second generation Nexus 7 has been discontinued, at least from the Play Store, so the options for purchasing a tablet with vanilla Android have been reduced to just the Nexus 9. While the Nexus 7 was released about a year and a half, its hardware is still very capable and has been updated to Android Lollipop, its screen remains as one of the most pixel-dense for a tablet. So if you're interested in getting one, you could probably find it at some retailers but the remaining units could be sold out soon. It has been reported that the Nexus program has recently seen a decline in sales, so Google will probably reevaluate the strategy that works for the best.