Question: I'm not a big fan of spending 100ish dollars to buy all three core rulebooks. Are there monster stats to be found online? Also, is there an online substitute for the DMG (for items)?

Answer: 
There are a few things. 

* The basic rules for [players](http://media.wizards.com/2015/downloads/dnd/BasicRules_Playerv3.4.pdf) and [Dungeon Masters](http://media.wizards.com/2015/downloads/dnd/DMBasicRules.pdf) provide all the information needed to start play, but not much in the way of monster stats.
* The [Systems Reference Document](http://media.wizards.com/2016/downloads/SRD-OGL_V1.1.pdf) ("the SRD") includes a subset of the monsters from the Monster Manual and the magic items in the Dungeon Master's Guide. All of the information from the SRD can be found (and searched) on [open5e](http://open5e.com/), which may be more convenient than a monolithic PDF.
A site called [Open5e](http://open5e.com/) recently launched that has everything from the SRD: rules, GM guide, character creation guide, spell list, some monsters, and equipment. 

It's easily searchable and it's open source, so people can contribute more info if there's anything they've missed.