I enjoy dabbling in Home Automation. Though, it is expensive, so I'll have to grow my home AI in small chunks. As I've been bargain shopping online over the last year, there are two smart bulbs that are consistently at a great, low cost.
SYLVANIA Dim Smart+ LED Light Bulb
This bulb has just recently started to hit a low price. Periodically, you can see it drop down to under $10. You will have to have a hub for this bulb to be smart however. For me, even though I'm converting my home into a Google Home system, I still have the Samsung Smartthings for my Hub. Which is good still since Google Assistant works with Samsung Smartthings.
You can see this great cost here on Amazon...
Singled Smart LED
This is my favorite bulb so far. I have several of these through out my house. It has always been $10 per bulb, but you can catch it a couple of dollars cheaper sometimes if you're watching. This bulb is also compatible with Samsung Smartthings. But, even better it's compatible directly with Google Assistant. It works best when it's connected with a google home device, like the Home or Mini. For example, I have two of these bulbs in my Man Cave and I have them tied to the Google Home Mini in that room within the Google Home App. Therefore, when I give a command in that room, I do not have to be specific to the bulbs. So, instead of saying, "Hey Google, turn off the Man Cave lights", I just need to say, "Hey Google, turn off the lights". Since the Home Mini in my room is the one that picked up my command, it knows to turn off the lights in the same room. Of course, I can still control the other lights while I'm in my room. Like, "Hey Google, turn off the Kitchen Lights." Or, "Hey Google, lock all of the doors", or "Hey Google, arm Nest Guard."
You can see this great bulb on Amazon as well...
One more benefit that I must tell you. Keep in mind that these are LED bulbs. So, they're lifespan is normally around 15 to 20 years or so. So if you think a single bulb for $10 is pricey, keep in mind that you wouldn't need to replace it for a very, very long time.