It may be cheaper to build, but it won’t be cheap to run. Wi-Fi eats batteries. The Arlo Wi-Fi cameras for example typically need new batteries every two or three weeks.
That may be fine for you, it depends on the use case, but there’s a reason why there are very few battery operated Wi-Fi devices now.
As we discussed in the dash topic, you pay seven times more for the BLE flic button then you do for the WiFi Dash button, but it’s likely you will get 60 times more battery life out of the Flic, plus it’s very hard to change the batteries in the dash.
Amazon marketed the Dash button as a replenishment gadget, so it’s likely that people would only be using it once or twice a month. That would give it about a two-year battery life. But if you’re using it as a doorbell or switch where it gets activated multiple times a day, it’s going to die fast.
If you just want to play around with it for fun, go for it. But if you’re looking for practical, reliable home automation switches and buttons, battery-operated Wi-Fi is unlikely to meet the need.