I recently posted on another thread about the SCT MX Gov't maps - the official road maps from which other map producers get their maps. These maps are online as .pdf files and can be downloaded for free. In real life at 100% size they are like regular folding road maps about 3 feet square so at 100% they are too large to see in you computer. But you can move around to look at various areas. There are maps of each state. We download them all. The last updates were done in 2012 so they are more up to date than anything else out there that I know off . . .
http://www.sct.gob.mx/informacion-general/planeacion/atlas-cartograficos/listado-de-atlas . . . . .
That said - we also have GPS - both a 7" Garmin that comes loaded with Mexico maps for about $220 - and Microsoft Streets & Trips 2013 which can be found online for between $20 to $40 depending on if they have a sale - to use as a planning map - or for about $80 get it with a GPS receiver and you can use it as a GPS - or you can buy other GPS receivers that will work with Streets & Trips and may or may not be better than the one Microsoft sells - most popular seems to be the Global Sat BU-353S4 for about $40.
A few years ago I created a basic tutorial for Streets & Trip which is now a little out of date but could be useful to get started - can be found online at . . .
http://www.rvtechlibrary.com/electronics/gps_streets_trips.htm
Specific directions about places you might want to go and things you might want to do can be found here by asking questions and by asking questions of those you meet along the way.