A friend needs wireless, potentially arduino-based, help

A buddy of mine who doesn't currently do HA but is heavy into robotics, makers club, wants to dip his toe in.
 
His first goal is wireless doorbells ringing multiple speakers, but will then be moving onto a few other areas:
A) Water leak detectors and solenoid valve
B) Aquaponics monitoring and control (sensor reading, relay actuation)
C) Interface to nest (?)
 
 
He also sent me this message:
Analog sensors (ammonia level, dissolved oxygen, temperature) and some switches (flow switches level switched), digital outputs (can't think of any analog outputs needed) but it would be cool to pass values back from an ardiuno so the arduino does most of the control. This is less important as I could just do a wifi version of this. 
 
He was initially looking into zWave potentially paired with SmartThings but I waved him off that as
[SIZE=12.8px]1) SmartThings = multi second lag time which is awful for a doorbell[/SIZE]
[SIZE=12.8px]2) zWave = not 100% reliable, which for Water leak/valve shutoff is bad[/SIZE]
 
[SIZE=12.8px]My experience in the high reliability space is with things that are overkill (ie Elk) but pre-built.  I'll point him here, but does anyone have any ideas in the "cheaper even if he has to do more legwork" space?[/SIZE]

Check out mysensors.org.
 
Cheers
Al

Been tinkering here with those el cheapo OpenWRT microuters.  The last one purchased was made and sold for tinkering with GPIO pins and an easy way to do Digital IO.  It is smaller than a regular sized Arduino (1" X 2") and you could even install an arduino nano inside of these devices.  Built in are wireless 802.XX and a couple of Ethernet ports.  They clock over 600Mhz these days.

For cheap it's hard to beat an arduino uno (clones available for $7) plugged into a Raspberry Pi (about $30).  Add wifi for another $7 or so.  You didn't say what sort of wireless or have any power limitations and said "cheaper but more legwork" so I think that fits the bill.  If he is involved in robotics and maker stuff he should be able to find help in those groups.  There are also lots of examples on the net of similar things.  Delays may be an issue for some things with this hardware.

awesome thanks for the tips. I've pointed him here, he hasn't yet decloaked, but if he has any questions then (dude post your own damn questions i'm not your secretary!)