Site lists the Core with embedded chip antenna at $39, which is about the cost of a $35 Trinket 6-pack (http://www.adafruit.com/products/1509). Granted those lack connectivity, but I think there's a sweet spot for something in between (i.e., with built-in BLE), maybe along the lines of these: https://www.kickstarter.com/projects/2016620887/mcthings-tin...

Either way the Spark looks nice, and the extra cost is sure to be recoverable in developer time.